md: bad block list should default to disabled.

commit 486adf72ccc0c235754923d47a2270c5dcb0c98b upstream.

Maintenance of a bad-block-list currently defaults to 'enabled'
and is then disabled when it cannot be supported.
This is backwards and causes problem for dm-raid which didn't know
to disable it.

So fix the defaults, and only enabled for v1.x metadata which
explicitly has bad blocks enabled.

The problem with dm-raid has been present since badblock support was
added in v3.1, so this patch is suitable for any -stable from 3.1
onwards.

Reported-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>