Cluster: don't forget yourself with CLUSTER FORGET.
Cluster: redis-trib help output improved.

Show options if any. Clarify that for some command any node address is
ok.
Cluster: don't let a node forget its own master.

redis-trib should make sure to reconfigure slaves of a node to remove
from the cluster to replicate with other nodes before sending CLUSTER
FORGET.
Cluster: redis-trib delnode implementation.