harness: Print better error messages on error conditions in 22.t
    
    These should help diagnose problems when dealing with error failures.
    In particular this helped distinguish the problem with io_pgetevents()
    not being implemented and it failing due to the sigset_t layout bug.
    
    Signed-off-by: Guillem Jover <guillem@hadrons.org>
    [JEM: fix up 80 columns violations]
    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>