inspection: Handle MD devices in fstab

This patch fixes inspection when fstab contains devices md devices
specified as /dev/mdN. The appliance creates these devices without reference to
the guest's mdadm.conf so, for e.g. /dev/md0 in the guest will often be created
as /dev/md127 in the appliance. With this patch, we match the uuids of detected
md devices against uuids specified in mdadm.conf, and map them appropriately
when we encounter them in fstab.