rcstream: add 'stream' subcommand to rcstreamctl

Running 'rcstreamctl stream' connects to redis and PSUBSCRIBEs to 'rc.*', as a
quick way of debugging whether edits are streaming in.

Change-Id: Ib585234564939275af75af8627c56e5e9f0dd5df
Merge "rcstream: add 'stream' subcommand to rcstreamctl" into production