Add new disk to clustered array

Algorithm:
1. Node 1 issues mdadm --manage /dev/mdX --cluster-add /dev/sdYY
2. Node 1 sends NEWDISK with uuid
3. Other nodes issue kobject_uevent_env with uuid
(Steps 4,5 could be a udev rule)
4. In userspace, the node searches for the disk using blkid -t SUB_UUID=""
5. Other nodes issue either of the following depending on whether the disk
   was found:
   mdadm --manage /dev/mdX --cluster-missing
   mdadm --manage /dev/mdX --cluster-confirm /dev/sdX
6. Other nodes drop lock on no-new-devs (CR) if device is found
7. Node 1 attempts EX lock on no-new-devs
8. If node 1 gets the lock, it sends METADATA_UPDATED after unmarking the disk
   as SpareLocal
9. If not (get no-new-dev lock), it fails the operation and sends METADATA_UPDATED
9. Other nodes follow suit (Currently not working for node who says --cluster-confirm if one other node says --cluster-missing)