Add multiple source file and templating support to file.append (#6905)

Allow states/file.append() to use multiple source files and templating
to generate the text to be appended to the 'named' file.
Update Docstring
Remove the warning about bug #7290 now its fixed.
Merge pull request #7296 from mech422/add-file-append-template-support

Add multiple source file and templating support to file.append (#6905)
Revert "salt-ssh still only supports glob, take out the extra target options"

This reverts commit cf9b241e945654ee85abe72d173028e889b58b6f.
Fix typo - its 'source_hashes' not 'soures_hash'
Add spaces to fixup pylint warnings
found another missing 'space'
Add cleaner explanation of environment mapping

Explicitely state that the 'master' branch is automagically mapped
to the 'base' environment.

Also mention the fact that top.sls files are merged from the different
branches, which suggests a setup where top.sls is only present in
the 'master' branch.
Make systemd>=207 hosts use /etc/sysctl.d/99-salt.conf

As of systemd 207, /etc/sysctl.conf is now ignored, and
/etc/sysctl.d/*.conf are used. This commit makes linux hosts check to
see if they are running systemd, and for new enough versions it uses
/etc/sysctl.d/99-salt.conf for the default config file.
Change default parms to None instead of mutable []
Merge pull request #7364 from mech422/add-file-append-template-support

Add file append template support - Fix typo and pylint errors
Merge pull request #7363 from terminalmage/issue7351

Make systemd>=207 hosts use /etc/sysctl.d/99-salt.conf
Merge pull request #7362 from piffio/gitfs-documentation-tips

Add cleaner explanation of environment mapping
Enable PEP263 pylint plugin. Fixes #7294.