harness: Skip the test if io_pgetevents() is not implemented
    
    Either the kernel or the syscall wrapper will return -ENOSYS when this
    syscall is not implemented. So we should cope with this in the test
    suite and SKIP the test case.
    
    This is currently the case for alpha and ia64, even though they have
    already been wired up very recently in the kernel mainline.
    
    Signed-off-by: Guillem Jover <guillem@hadrons.org>
    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>