based on #275

fixes #274

Also, check config before applying

* correctly set dependencies in configuration
* update RPM repo key
* add tests for passenger installation as nginx module
* update test matrix

* Semi-automated using `ssf-formula` (v0.5.0)
* Fix errors shown below:

```bash
nginx-formula$ $(grep "\- yamllint" .travis.yml | sed -e "s:^\s\+-\s\(.*\):\1:")
pillar.example
  5:1       warning  missing document start "---"  (document-start)
  6:89      error    line too long (110 > 88 characters)  (line-length)
  7:89      error    line too long (99 > 88 characters)  (line-length)
  19:89     error    line too long (132 > 88 characters)  (line-length)
  35:25     warning  truthy value should be one of [false, true]  (truthy)
  36:89     error    line too long (106 > 88 characters)  (line-length)
  40:89     error    line too long (115 > 88 characters)  (line-length)
  43:16     warning  truthy value should be one of [false, true]  (truthy)
  44:89     error    line too long (105 > 88 characters)  (line-length)
  48:16     warning  truthy value should be one of [false, true]  (truthy)
  54:14     warning  too few spaces before comment  (comments)
  57:13     warning  truthy value should be one of [false, true]  (truthy)
  57:18     warning  too few spaces before comment  (comments)
  58:14     warning  too few spaces before comment  (comments)
  60:5      warning  missing starting space in comment  (comments)
  60:89     error    line too long (96 > 88 characters)  (line-length)
  61:89     error    line too long (90 > 88 characters)  (line-length)
  62:89     error    line too long (90 > 88 characters)  (line-length)
  63:89     error    line too long (94 > 88 characters)  (line-length)
  64:5      warning  missing starting space in comment  (comments)
  64:89     error    line too long (96 > 88 characters)  (line-length)
  68:9      error    wrong indentation: expected 10 but found 8  (indentation)
  76:9      error    wrong indentation: expected 10 but found 8  (indentation)
  86:9      error    wrong indentation: expected 10 but found 8  (indentation)
  90:14     warning  too few spaces before comment  (comments)
  90:89     error    line too long (104 > 88 characters)  (line-length)
  92:6      warning  missing starting space in comment  (comments)
  92:89     error    line too long (106 > 88 characters)  (line-length)
  94:89     error    line too long (104 > 88 characters)  (line-length)
  97:6      warning  missing starting space in comment  (comments)
  97:89     error    line too long (106 > 88 characters)  (line-length)
  100:62    warning  too few spaces before comment  (comments)
  100:89    error    line too long (121 > 88 characters)  (line-length)
  101:62    warning  comment not indented like content  (comments-indentation)
  101:89    error    line too long (116 > 88 characters)  (line-length)
  102:89    error    line too long (112 > 88 characters)  (line-length)
  103:89    error    line too long (99 > 88 characters)  (line-length)
  105:89    error    line too long (124 > 88 characters)  (line-length)
  106:8     warning  missing starting space in comment  (comments)
  106:89    error    line too long (117 > 88 characters)  (line-length)
  112:89    error    line too long (97 > 88 characters)  (line-length)
  120:31    warning  missing starting space in comment  (comments)
  123:89    error    line too long (95 > 88 characters)  (line-length)
  127:13    error    wrong indentation: expected 14 but found 12  (indentation)
  151:33    warning  too few spaces before comment  (comments)
  151:89    error    line too long (94 > 88 characters)  (line-length)
  152:22    warning  too few spaces before comment  (comments)
  152:89    error    line too long (90 > 88 characters)  (line-length)
  153:21    warning  too few spaces before comment  (comments)
  153:89    error    line too long (101 > 88 characters)  (line-length)
  154:22    warning  too few spaces before comment  (comments)
  155:18    warning  too few spaces before comment  (comments)
  155:89    error    line too long (103 > 88 characters)  (line-length)
  163:89    error    line too long (100 > 88 characters)  (line-length)
  164:89    error    line too long (106 > 88 characters)  (line-length)
  165:18    warning  truthy value should be one of [false, true]  (truthy)
  167:89    error    line too long (109 > 88 characters)  (line-length)
  170:10    warning  missing starting space in comment  (comments)
  172:10    warning  missing starting space in comment  (comments)
  172:89    error    line too long (120 > 88 characters)  (line-length)
  173:10    warning  missing starting space in comment  (comments)
  173:89    error    line too long (118 > 88 characters)  (line-length)
  174:89    error    line too long (120 > 88 characters)  (line-length)
  175:20    warning  truthy value should be one of [false, true]  (truthy)
  175:89    error    line too long (102 > 88 characters)  (line-length)
  177:89    error    line too long (100 > 88 characters)  (line-length)
  178:89    error    line too long (101 > 88 characters)  (line-length)
  182:13    error    wrong indentation: expected 14 but found 12  (indentation)
  184:15    error    wrong indentation: expected 16 but found 14  (indentation)
  186:15    error    wrong indentation: expected 16 but found 14  (indentation)
  189:15    error    wrong indentation: expected 16 but found 14  (indentation)
  193:9     warning  comment not indented like content  (comments-indentation)
  196:13    error    wrong indentation: expected 14 but found 12  (indentation)
  198:15    error    wrong indentation: expected 16 but found 14  (indentation)
  202:15    error    wrong indentation: expected 16 but found 14  (indentation)
  206:9     warning  comment not indented like content  (comments-indentation)
  218:16    warning  too few spaces before comment  (comments)
  218:89    error    line too long (96 > 88 characters)  (line-length)
  219:18    warning  truthy value should be one of [false, true]  (truthy)
  223:57    warning  too few spaces before comment  (comments)
  223:89    error    line too long (111 > 88 characters)  (line-length)
  224:57    warning  comment not indented like content  (comments-indentation)
  224:89    error    line too long (118 > 88 characters)  (line-length)
  226:89    error    line too long (90 > 88 characters)  (line-length)
  236:18    warning  truthy value should be one of [false, true]  (truthy)
  245:89    error    line too long (108 > 88 characters)  (line-length)
  252:89    error    line too long (104 > 88 characters)  (line-length)
  305:89    error    line too long (115 > 88 characters)  (line-length)
  306:32    error    trailing spaces  (trailing-spaces)

test/salt/default/pillar/nginx.sls
  1:1       error    too many blank lines (1 > 0)  (empty-lines)
  7:1       warning  missing document start "---"  (document-start)
  11:9      error    wrong indentation: expected 10 but found 8  (indentation)
  23:18     warning  truthy value should be one of [false, true]  (truthy)
  24:18     warning  truthy value should be one of [false, true]  (truthy)
  28:18     warning  truthy value should be one of [false, true]  (truthy)
  31:13     error    wrong indentation: expected 14 but found 12  (indentation)
  33:15     error    wrong indentation: expected 16 but found 14  (indentation)
  36:15     error    wrong indentation: expected 16 but found 14  (indentation)
  38:1      error    too many blank lines (1 > 0)  (empty-lines)
```

(...) for snippets filename.
BREAKING CHANGE: Users have to modify their pillar
according to this commit. Users MUST append '.conf' for their
existing managed snippets.

BREAKING CHANGE: all previous `nginx` based configurations must be reviewed;
`nginx.ng` usage must be promoted to `nginx` and any uses of the original
`nginx` will have to be converted.