Need a way to take node offline

We need a way to take down a node without un-configuring for maintenance (mostly a collector in multi-collector configuration). The node should be brought back up on restart. Unconfiguring the node, while an option, requires entering the configuration information again. Alternatively a command like `exec shutdown physicalnode` will shutdown any logical node on the machine (flush the output, stop input) and optionally terminate the Flume process. The same may apply to master or an agent (an agent will have to stop accepting or reading the data). Currently we can just shut down the Java process on machine, which potentially leads to either data loss or data duplication in different modes.