[XFS] optimize dmapi event tests w/o dmapi config

SGI-PV: 969372
SGI-Modid: xfs-linux-melb:xfs-kern:29444a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Vlad Apostolov <vapo@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>