xfs: skip tests if formatting small filesystem fails

xfs: skip tests if formatting small filesystem fails

There are a few tests that try to exercise XFS functionality with an
unusually small (< 500MB) filesystem.  Formatting can fail if the test
configuration also specifies a very large realtime device because mkfs
hits ENOSPC when allocating the realtime metadata.  The test proceeds
anyway (which causes an immediate mount failure) so we might as well
skip these.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>