Improve exclude_nodes cmds to manage a list of nodes and take add/remove lists of nodes

[slmingol]

Today these cmds only can deal w/ 1 node. Improve em so you can give a single or csv list of short node prefixes and it'll go figure out IPs and add them to the exclude lists.

show_excluded_nodes                            # show excluded nodes from cluster
exclude_node_name                              # exclude a node from cluster (node suffix),
clear_excluded_nodes                           # clear any excluded cluster nodes