imsm: fix activate spare to ignore foreign disks

imsm: fix activate spare to ignore foreign disks

A foreign disk is one that all other drives believe is not-in-sync but
does not have the 'failed' status bit set.

This also reverts, because that commit is addressing the wrong problem.
Ideally mdmon would kick "non-fresh" drives like the kernel does at
native-md activation time, but that is too awkward to implement at the
moment because mdadm owns container manipulations.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>