apiserver: TestAgentConnectionsShutDownWhenStateDies is very slow

[Andrew Wilkins]

This test takes 60s to run (on my machine; should be more or less the same on any machine). I've investigated the issue, and found that it's due to the presence pinger on connection termination.

What happens is this:
 1. test kills mongo
 2. apiserver's mongo pinger finds mongo is dead, initiates connection termination
 3. connection termination code runs resource cleanups
 4. machine pinger resource's cleanup calls the presence pinger's Stop(), and then Kill() methods

The presence.Pinger.Kill() method is hanging around for 30s (x2 -- one in the test, one in the tear down) because it's waiting for a connection (the timeout is 30s).

[Andrew Wilkins (axwalk)]

Probably what we should do is, when the mongo connection is known to be dead, not attempt to Kill() the presence.

[Andrew Wilkins (axwalk)]

Hooray, shaved 60s off the apiserver package tests. Only 120s to go.