1. Message and message index table db writes were happening without going
   through rate limits set for db queue and hence contrail-collector would
   end up having huge db queues and high memory usage when
   contrail-vrouter-agent was sending AgentRouteLog in a loop due to
   route flaps/another unrelated bug. libstdc++ default allocator
   does not release memory back to the OS and hence contrail-collector
   would seem to have a memory leak due to the above scenario.
2. Add rates limits in sandesh client state machine and in collector per
   generator state machine and db queues even for SYS_EMERG messages.

Change-Id: I9cb0eb3a9e673a23f6f2ad8c345aa5982d293f8c
Closes-Bug: #1391757