Fix PR build and doc push commit message
    
    OpenShift Build Strategy doesn't build Pagure pull-requests because Pagure PRs
    follow `pull/<PR No.>/head` format and there is no options in OpenShift BuildConfig
    to specify custom refspec like `+refs/pull/*/head:refs/remotes/origin/pull/*/head`.
    
    This PR will change the way of tracking a Git commit with ref name to work around this issue,
    although the actual commit behind a Git ref may change during multiple
    Git checkouts.