CentOS 6.5 improvements.

The changes in this PullRequest add improvements to running GitLab through Salt on CentOS 6.5, 
as well as the ability to use a MySQL database instead of Postgresql.
This (and the matching postgresql call) may need modification if the databse is running on another host. https://github.com/viq/gitlab-formula/pull/6/files#diff-a6ad60a209aae8927b864383bf9e2b8fR94 is one way to go about it.