Improve ServiceBus/EventHub listener shutdown

[mathewc]

Recent changes addressing work item #1703 now log all background errors coming from the SB MessageReceiver. This works in ensuring errors are logged during message processing.

However, during normal host shutdown, it seems disposal ordering is causing spurious errors to be logged, when there isn't a problem. E.g. the host is shutting down, the listener is stopped/disposed, and the MessageReceiver attempts one final receive operation but fails because everything is being disposed. See ICM incident #73280007.

We should clean this up so that these errors aren't logged when the host is being disposed.

See related issue: #1784

[mathewc]

Check EventHub listener shutdown as well, since it follows the same eventing pattern

[fabiocav]

@mathewc is this done? The PR has been merged.

[mathewc]

The issue is still open because I haven't merged this to dev yet, only v2.x. I'll do that today