Monitor: don't complain about non-monitorable arrays in mdadm.conf

Monitor: don't complain about non-monitorable arrays in mdadm.conf

If we are asked to monitor a RAID0 or Linear - which cannot be
monitored - we complain with "Device Disappeared .... Wrong-Level".

However if the RAID0 or Linear is being requested because it is
in mdadm.conf then the message is inappropriate and confusing.

So track which arrays are added from the config file, and suppress
that message in that case.

Reported-by: "Johnson Yan" <johnson_yan@usish.com>
Signed-off-by: NeilBrown <neilb@suse.de>