fuzzy: skip online scrub and health checks if not supported

fuzzy: skip online scrub and health checks if not supported

Commit a27e6e6f4c18 introduced xfs health checking on no-repair fuzz,
which in turn requires scrub to be run before that. The health checks
are done only if scrub returns with an error (which is expected as an
indication that fuzzed metadata errors were picked up), but the code
does not discern between xfs_scrub returning an error because of
uncorrected metadata vs failing because the kernel does not support
scrub at all.

This causes all tests that do fuzzing with no-repair strategy to fail on
kernels compiled without online scrub support (CONFIG_XFS_ONLINE_SCRUB).

Skip scrub and health checks altogether, if the kernel does not support
it, since the tests are still valuable.

Fixes: a27e6e6f4c18 ("common: check xfs health after doing an online scrub")
Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>