xfs: force unlink metadata updates to disk

xfs: force unlink metadata updates to disk

In xfs/318 and xfs/325 we inject errors on extent freeing then delete
some files to see if we can make the filesystem go offline.  However,
with the advent of deferred inode inactivation, sync won't guarantee
that unlinked inodes removal is actually pushed to disk since the "inode
needs to be deallocated" state is persisted to disk.  Freeze achieves
this, however, so inject a freeze/thaw cycle to make sure we hit the
injected error.

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