Resolve "Gitlab Shell no longer uses repository path"

Closes #2194 (closed)

1. Move identification of Gitlab['gitlab_rails']['repositories_storages'] from git_data_dirs to gitaly library.
   1. Move conversion of git_data_dir, string form of git_data_dirs to hash form of git_data_dirs to gitaly library from gitlab-shell library
   2. Split out conversion as a separate method so there is no need of a temporary variable to hold the result
2. Move creation of git_data_dirs and git_data_dirs/repositories to gitlab-rails recipe.
   • Because if this was moved to gitaly recipe and someone disabled gitaly, the directories won't get built.
3. Fix specs to match these changes