xfs/077: fix test for userspace meta_uuid support

xfs/077: fix test for userspace meta_uuid support

The current _require_meta_uuid() test looks for a failure return
code from xfs_db -x -c "uuid generate" but in fact this exits
with success.  (In fact uuid_f always exits with success; perhaps
this needs fixing, but that's in the wild now).

So grep for the string(s) stating that it failed, instead.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>