Event socket changes for rbczmq/to make testing easier.

- Use the rbczmq API for the event socket.
- Split out the event socket setup into a public method
- Call the setup by default from #run so it doesn't get touched by
  tests.
- Call #setup_event_socket from tests that explicitly test events
- Make tests use an ephemeral port to avoid collision with a real
  event socket on the same machine.
Bump strelka dependency