Move channel mbean registration/deregistration to ChannelService.start/stop.
This lets us get remove that hacky map of channels in JChannelFactory.
ChannelService no longer connects/disconnects the channel - so it doesn't need asynchronous start/stop.
Merge pull request #6155 from pferraro/jgroups

Move channel mbean registration/deregistration to ChannelService.start/stop.