Monitor: don't add more spares than needed

Monitor: don't add more spares than needed

When we add a spare to a container it takes a while
before it is noticed by mdmon and recovery starts.
During this time the array remains degraded but we don't want to add
any more spares to this container. Therefore we must check container
with degraded array if it doesn't already have a suitable spare.
container_choose_spare is reused with from=to
Domain check is not needed in this situation.

Ping_manager after moving disk is needed to be able to see
newly added disk in container after coming back through the loop.

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