Couple of fixes for the mirroring-in feature
    
    This commit does a couple of fixes in the code used for the mirroring-in
    feature.
    It ensures any exception thrown by pagure.lib.git.mirror_pull_project are
    caught and properly logged. Otherwise, the script dies in the middle of
    the processing.
    It also checks that there is a remote before doing anything and if there
    is no remote, it just bails.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr></pingou@pingoured.fr>