common/xfs: skip xfs_check unless the test runner forces us to

common/xfs: skip xfs_check unless the test runner forces us to

At long last I've completed my quest to ensure that every corruption
found by xfs_check can also be found by xfs_repair.  Since xfs_check
uses more memory than repair and has long been obsolete, let's stop
running it automatically from _check_xfs_filesystem unless the test
runner makes us do it.

Tests that explicitly want xfs_check can call it via _scratch_xfs_check
or _xfs_check; that part doesn't go away.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>