Lint mediawiki_singlenode module

I'd like to migrate some patches from MediaWiki-Vagrant to this module. But
first -- code style!

- Single quotes unless interpolating variable.
- 'ensure' should be the first parameter, if present, per Puppet style guide.
- When resources are specified as dependencies, every word needs to be
  capitalized ('Git::Clone').
- I assumed 'hostname' and 'labs_mediawiki_hostname' are defined in top scope
  and thus specified them as '$::hostname' and '$::labs_mediawiki_hostname'.
- Other misc. things suggested by puppet-lint and the puppet style guide.

I haven't tested this, sorry.

Change-Id: Ib39a9b5a39ea443cba15f472694fca99d01a12b9
Merge "Lint mediawiki_singlenode module" into production