juju/api: don't warn on aborted connection

juju/api: don't warn on aborted connection

I've been playing with Roger's tweak to using cached API addresses
rather than determining them by reading the provider-state file. It
works, but it has a bug that when it successfully connects to the API
with the cached information, it causes the other goroutine to stop
with an "aborted" exception. That was being displayed to the user as a
WARNING which is pretty clearly incorrect. I can understand that we
don't want to silently consume errors, but errAborted should be
treated as control flow logic.

So I made that happen. I wanted to add testing that we output sane
information to the user, but it was clumsy to find the right hook
points. If people feel strongly I can try to track that down, but I
didn't want to lose the patch in flight.

https://code.launchpad.net/~jameinel/juju-core/tweak-cached-address-functionality/+merge/192789

(do not edit description out of merge proposal)

[jameinel, 2013-10-26 16:55:02]

Please take a look.

[gz, 2013-10-31 09:15:05]

LGTM.

https://codereview.appspot.com/17700043/diff/1/juju/api.go
File juju/api.go (right):

https://codereview.appspot.com/17700043/diff/1/juju/api.go#newcode36
juju/api.go:36: var errAborted = fmt.Errorf("aborted")
Er... is this really the best way of doing this? I guess so.