Fix #495

Make the upstream salt package repository selectable, thus allowing the
use of archived salt versions (hosted in
https://archive.repo.saltproject.io), as well as custom salt versions
hosted in alternate repositories.

* CVE-2021-25283 enables Jinja2 safe mode, which breaks use of
  `'dict' in x.__class__.__name__` workaround
* Workaround no longer needed as CentOS 6 is EOL

Use ugly `zypper lr --uri` hack to get around failure if the `base_url`
already exists under a different name:

```
      ID: salt-pkgrepo-install-saltstack-suse
Function: pkgrepo.managed
    Name: systemsmanagement_saltstack_products
  Result: False
 Comment: Failed to configure repo 'systemsmanagement_saltstack_products':
          Repository 'systemsmanagement_saltstack_products' already exists as 'systemsmanagement_saltstack'.
 Started: 09:28:39.154054
Duration: 2760.727 ms
```

Upstream code:

* 45cc49daed/salt/modules/zypperpkg.py (L1262-L1265)

* Semi-automated using https://github.com/myii/ssf-formula/pull/285

When running a high-state on the salt-master to deploy itself, the run fails
with an Authentication error occurred because the master restarts half way though.

* Automated using https://github.com/myii/ssf-formula/pull/237

* add `-` if someone supplies `py3` in pillar, like other platforms

X

Available only on Debian family OS-es

Instead of the default service.running + enabled, you can control
the actual state, via pillar.
And you can even say 'state = ignore' and no state will be generated
to control the service

* Checked using https://github.com/myii/ssf-formula/pull/131

```bash
Examining salt/syndic.sls of type state
[201] Trailing whitespace
salt/syndic.sls:12
  {%- endif %}
```

```bash
Examining salt/minion.sls of type state
[210] Numbers that start with `0` should always be encapsulated in quotation marks
salt/minion.sls:20
    - mode: 0644
```

```bash
Examining salt/map.jinja of type state
[209] Jinja comment should have spaces before and after: {# comment #}
salt/map.jinja:4
{## Start imports ##}

[209] Jinja comment should have spaces before and after: {# comment #}
salt/map.jinja:21
{## Merge in salt pillar ##}

[209] Jinja comment should have spaces before and after: {# comment #}
salt/map.jinja:24
{## Merge in salt_formulas pillar ##}
```

* Semi-automated using https://github.com/myii/ssf-formula/pull/31
* Includes:
  - Update TOFS
  - Use `bin/kitchen`
  - Use `dist: bionic` in Travis
  - Add `yamllint` and apply rules
  - Use `pillars_from_files` throughout
  - Replace EOL images in Kitchen & Travis
  - Add `develop` images in Kitchen & Travis
* Fix (or ignore)  errors shown below:

```bash
salt-formula$ yamllint -s .
./pillar.example
  1:1       warning  missing document start "---"  (document-start)
  5:23      warning  truthy value should be one of [false, true]  (truthy)
  8:25      warning  truthy value should be one of [false, true]  (truthy)
  11:25     warning  truthy value should be one of [false, true]  (truthy)
  19:21     warning  truthy value should be one of [false, true]  (truthy)
  40:89     error    line too long (108 > 88 characters)  (line-length)
  41:89     error    line too long (112 > 88 characters)  (line-length)
  43:89     error    line too long (112 > 88 characters)  (line-length)
  45:89     error    line too long (110 > 88 characters)  (line-length)
  47:89     error    line too long (89 > 88 characters)  (line-length)
  74:27     warning  truthy value should be one of [false, true]  (truthy)
  82:9      error    wrong indentation: expected 10 but found 8  (indentation)
  101:14    warning  truthy value should be one of [false, true]  (truthy)
  102:20    warning  truthy value should be one of [false, true]  (truthy)
  103:89    error    line too long (119 > 88 characters)  (line-length)
  121:7     warning  comment not indented like content  (comments-indentation)
  122:24    error    syntax error: found character '%' that cannot start any token
  310:89    error    line too long (102 > 88 characters)  (line-length)
  330:89    error    line too long (113 > 88 characters)  (line-length)
  433:1     error    too many blank lines (1 > 0)  (empty-lines)

./salt/osmap.yaml
  4:2       error    syntax error: found character '%' that cannot start any token
  6:89      error    line too long (93 > 88 characters)  (line-length)
  22:89     error    line too long (137 > 88 characters)  (line-length)
  23:89     error    line too long (134 > 88 characters)  (line-length)
  33:89     error    line too long (149 > 88 characters)  (line-length)
  34:89     error    line too long (146 > 88 characters)  (line-length)

./salt/osfamilymap.yaml
  4:2       error    syntax error: found character '%' that cannot start any token
  6:89      error    line too long (94 > 88 characters)  (line-length)
  24:89     error    line too long (149 > 88 characters)  (line-length)
  25:89     error    line too long (146 > 88 characters)  (line-length)
  39:89     error    line too long (105 > 88 characters)  (line-length)
  40:89     error    line too long (127 > 88 characters)  (line-length)
  56:89     error    line too long (101 > 88 characters)  (line-length)

./salt/ospyvermap.yaml
  4:1       warning  missing document start "---"  (document-start)

./salt/defaults.yaml
  3:1       warning  missing document start "---"  (document-start)
  7:21      warning  truthy value should be one of [false, true]  (truthy)
  8:12      warning  truthy value should be one of [false, true]  (truthy)
  9:23      warning  truthy value should be one of [false, true]  (truthy)
  10:19     warning  truthy value should be one of [false, true]  (truthy)
  14:25     warning  truthy value should be one of [false, true]  (truthy)
  15:25     warning  truthy value should be one of [false, true]  (truthy)
  16:27     warning  truthy value should be one of [false, true]  (truthy)
  17:27     warning  truthy value should be one of [false, true]  (truthy)
  39:28     warning  truthy value should be one of [false, true]  (truthy)
  41:28     warning  truthy value should be one of [false, true]  (truthy)
  45:24     warning  truthy value should be one of [false, true]  (truthy)
  49:30     warning  truthy value should be one of [false, true]  (truthy)
  54:28     warning  truthy value should be one of [false, true]  (truthy)
  63:25     warning  truthy value should be one of [false, true]  (truthy)
  68:15     warning  truthy value should be one of [false, true]  (truthy)
```

This prevents the `return` key being duplicated in the minion config by L1205