SNMP Alarm Support

I think this is actually less difficult than you're expecting - I think you don't need a mocked ZMQ server, you just need to:
* mock out CommunicationMonitor, and test that when a HttpConnection (etc.) gets a success/error response, the appropriate method on CommunicationMonitor is called
* mock out AlarmReqAgent, and test that when enough CommunicationMonitor calls are made, the expected call to alarm_request is made

https://github.com/Metaswitch/cpp-common/blob/master/test_utils/test_interposer.hpp gives you control over time for these sorts of tests.