The current user might not be able to peek into the loop files directly,
use the helper. Discovered by running tests in travis.
Signed-off-by: David Sterba <dsterba@suse.com>
Testcase for "Btrfs-progs: fix btrfs-convert rollback to check
ROOT_BACKREF", make sure we don't try a rollback if the ext2_subvol is
half-deleted.
Signed-off-by: David Sterba <dsterba@suse.com>