generic: test error shutdown while stressing filesystem

generic: test error shutdown while stressing filesystem

Test log recovery with repeated (simulated) disk failures.  We kick
off fsstress on the scratch fs, then switch out the underlying
device with dm-error to see what happens when the disk goes down.
Having taken down the fs in this manner, remount it and repeat.
This test is a Good Enough (tm) simulation of our internal multipath
failure testing efforts.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>