Rails is required when only the gitaly service is enabled

The gitaly service depends on gitlab-shell/config.yml but currently it is not generated on the storage nodes. This is due to not enabling rails on the these VMs (because there is no reason to have rails enabled).

In order to work around this we need to set https://dev.gitlab.org/cookbooks/chef-repo/merge_requests/2349 which we currently understand to be an internal config parameter and not something that should ever be explicitly set to true in the gitlab.rb file.

There is a merge request to enable rails https://dev.gitlab.org/cookbooks/chef-repo/merge_requests/2349/diffs here as a workaround though this looks like it might be an omnibus issue since it would affect other deployments where gitaly is running on server without rails enabled.