[XFS] Catch errors when turning off quotas.

[XFS] Catch errors when turning off quotas.

When turning off quota, we need to write various transactions to the log
to ensure that they are cleanly removed in the case of a crash. We need to
check that the transactions hit the disk correctly. If we fail to write
the final quota off transaction, we are corrupt in memory and so the only
option is to shut the filesystem down at this point.

SGI-PV: 980084
SGI-Modid: xfs-linux-melb:xfs-kern:30790a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>