xfs: test XFS torn log write detection

xfs: test XFS torn log write detection

XFS torn log write detection includes a mechanism to inject CRC errors
into log records at runtime and shutdown the fs accordingly. This
ensures that the CRC verification pass on the subsequent mount discovers
an invalid record near the head of the log and considers it a torn
write.

This test runs a workload with error injection enabled and verifies that
the subsequent mount is successful. The test repeats for several
iterations using a random frequency factor for the error event each
time.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>