Code clean-up/refactor

Clean up some of the code to target [6-1-stable branch](https://github.com/gitlabhq/gitlabhq/blob/6-1-stable/doc/install/installation.md)

* Move gitlab.home to /srv/git - [FHS 2.3](http://www.pathname.com/fhs/pub/fhs-2.3.html)
* Use ruby_build to pull in 2.0.0-p247 by default per gitlabhq
  installation docs.
* Clean up both cookbook and package dependencies
* Remove ruby-shadow, included in Omnibus, not needed anyway as no
  password is set.
* Use gitconfig template, instead of execute
* Remove bundler/rake, not listed in installation
* Fix shebang on init template, causing foodcritic failure.