Fix apt key not being a key

This prevents the key from being constantly re-added everytime puppet is run
due to apt not detecting that the key is already present.
Make this similar to apt's so that we can actually test multiple copies
of ruby/puppet properly.
Rename gemfile to have a standard name.
Merge pull request #59 from apenney/travis

Make this similar to apt's so that we can actually test multiple copies
Merge pull request #32 from johnnyg/fix-apt-key

Fix apt key not being a key