mdadm: added --no-sharing option for Monitor mode

mdadm: added --no-sharing option for Monitor mode

--no-sharing option disables moving spares between arrays/containers.
Without the option spares are moved if needed according to config rules.
We only allow one process moving spares started with --scan option.
If there is such process running and another instance of Monitor
is starting without --scan, then we issue a warning but allow it
to continue.

Signed-off-by: Anna Czarnowska <anna.czarnowska@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>