Acquiring channel should not block graceful shutdown

[istreeter]

@pondzix I think we need this small amendment.

If we can't create the channel, then we expect kubernetes to eventually send a SIGTERM to the app. When that happens, we want the app to shutdown gracefully as quickly as possible.

But the acquire block of a resource is uncancelable. So instead of shutting down on the SIGTERM, it will continue to retry indefinitely (until Kubernetes eventually hard-kills it with a SIGKILL).

We can fix it by switching make to makeFull and then use the Poll so that the acquire is cancelable.