[WORKER] Support PING message

This change prepares the code to support a separation of the ping
functionality and a new statistics gathering call. This change will
see either the STATS action or the PING action as the same, so both
will be supported for the time being. Eventually, the STATS action
will have a different meaning and return info like bytes output.

Change-Id: Ib86893725818ce0e6fa57c0bb01ec6df56e4d48a