Older imsm arrays, or arrays created by something other than mdadm,
might have one of two unused bits in the attributes field set. If
they do, we need to ignore them, not fail to assemble the array.
Signed-off-by: Doug Ledford <dledford@redhat.com>
(cherry picked from commit 22ef59a98600f5900f957e2a0bdc16139aa528da)
