Try reducing the time the lock is needed
    
    It seems that mysql has issue deleting the project when the
    pagure.exceptions.RepoExistsException is raised because of lock
    timeout: Lock wait timeout exceeded; try restarting transaction
    
    So we tried reducing the time the lock is needed by just locking
    the part where it makes sense rather than the full function.
    From our empirical tests it worked, future will tell if it
    persists.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>