mdmon: don't use 'ghost' values from an inactive array.

It is possible for mdmon to see (in /proc/mdstat) and array
in 'inactive' state, "mdadm -S" has written "inactive" to
"array_state".

In this state values such as "raid_disk" are not meaningful
and so should be ignored by manage_member().

Reported-by: "Dorau, Lukasz" <lukasz.dorau@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>