btrfs: add support for capturing metadumps of corrupted fses

btrfs: add support for capturing metadumps of corrupted fses

Add the capability to capture btrfs metadumps when filesystem checks
fail, so that they can be used for further debugging. This is useful
for tests that _require_test and/or _require_scratch for which
filesystem checkers will run after a test completes and may
occasionally pick up inconsistencies.

Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>