xfs: test xfs_healer's event handling

Make sure that xfs_healer can handle every type of event that the kernel
can throw at it by initiating a full scrub of a test filesystem.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>