This implement the gossipier API. All actions perform on the local
gossiper.
The following functionality is supported:
/gossiper/downtime/{addr}
/gossiper/generation_number/{addr}
/gossiper/assassinate/{addr}
The following are extened API beyond the MBean definition:
/gossiper/endpoint/down
/gossiper/endpoint/live
Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>