xfs_scrub: fix handling of read-verify pool runtime errors

xfs_scrub: fix handling of read-verify pool runtime errors

Fix some bogosity with how we handle runtime errors in the read verify
pool functions.  First of all, memory allocation failures shouldn't be
recorded as disk IO errors, they should just complain and abort the
phase.  Second, we need to collect any other runtime errors in the IO
thread and abort the phase instead of silently ignoring them.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>