Standalone servers for keepalive and receiver

 - keepalive renamed to assasin (name conflicts) and starts as separate process controlled by supervisor
 - RPC receiver moved to separate server

Implements: blueprint nailgun-move-to-uwsgi

Change-Id: I75898a1975794a85e2335a1aa3dc56d073c3af39
Merge "Standalone servers for keepalive and receiver"