no option to force --incremental (re)add to active array

[ceg]

The --incremental call (as also done by udev rules) refuses to (re)add a temporarily disconnected members back to an already restarted (active) raid array.

# mdadm --incremental /dev/sdb1
mdadm: not adding /dev/sdb1 to active array (without --run) /dev/md/0

# mdadm --incremental --run /dev/sdb1
mdadm: failed to add /dev/sdb1 to /dev/md/0: Invalid argument.

Even though this refusal may in the future only happen for true conflicts (Bug #1088532), there is still an option missing to --force the addition anyway.

Using --force with --incremental (where mdadm will still apply sanity checks to not add it to a completely wrong array etc.) seems much less dangerous than forcing the user to have to --zero-superblock around in the system.