ci(kitchen+travis): use `py2` instead of `py3` for `centos-7`

* https://github.com/saltstack-formulas/salt-formula/pull/414

fix(gemfile): use latest `kitchen-salt`

Squashed from:

* pillar.example: an include was missing a colon
* pillar.example: 2 directives not indented properly
* pillar.example: added the stock log_format
* pillar.example: make log path match map.jinja
* pillar.example: worker_connections value from latest mainline nginx
* pillar.example: fixed other uses of include
* pillar.example: corrected formatting
* pillar.example: corrected log_format
* pillar.example: reset log_format to try another day

fix: corrected indentation on context in file.managed states

added default snippets directory for FreeBSD platform

Updated for Suse 15.0

Fix multiple values for the same key (include/listen) in server config file

With this one can now also write

 - include:
   - file1
   - file2

Rather than only

 - include: file1
 - include: file2

Fully document #193 stream module

Document pid_file pillar for nginx state (#96)

Fix sites-available bug in formula logic

Document issue 93 in pillar.example

Fix build deps for NGINX NG build from source

makedirs needed for 'available_dir' pillar

Fix #182 bug

Enforce PPA's on Ubuntu(s) only; not Debian

Document #122 solution in pillar.example

Disabled automatic sorting of mapping keys in jinja templating

Servers config should require available/enabled dirs

Add SUSE support and 2 small fixes

implement test harness

on openSUSE Leap 15.0, the string was systemd.cpython-36

like openSUSE and SLES

to reduce duplication of constants

deploy certificates directly from pillar

Snippets

Allow installation of multiple packages