Add loop helpers and simplify deploy example

[johnsca]

No description provided.

[tvansteenburgh]

Shouldn't this be loop.run(main()) ?

[johnsca]

Yes. Yes it should.

[johnsca]

The interrupt handling doesn't work like I expected and we get a bunch of error dumps. Also now getting an error on normal run that I don't understand:

Connecting to model
Deploying ubuntu
Waiting for active
Removing ubuntu
Disconnecting from model
Exception ignored in: <bound method BaseEventLoop.__del__ of <_UnixSelectorEventLoop running=False closed=True debug=False>>
Traceback (most recent call last):
  File "/usr/lib/python3.5/asyncio/base_events.py", line 431, in __del__
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 58, in close
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 139, in remove_signal_handler
  File "/usr/lib/python3.5/signal.py", line 47, in signal
TypeError: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object

[tvansteenburgh]

stop_loop could be changed to loop.stop

[tvansteenburgh]

I don't really understand the "signal handler must be callable" error either. Regarding errors at termination, I assume those are coming from still-running coroutines. You'll always get tracebacks if you stop the loop while any coroutines are still running. You can try canceling all running coroutines in your signal handler.

[johnsca]

@tvansteenburgh I tried cancelling the coroutines in various ways but couldn't avoid the errors, which is actually why I had the separate stop_loop functionality. I added one of my attempts to this PR, but it doesn't help.

[johnsca]

I got it working gracefully and (had to) boiled it down to a single helper function instead of split across three.

[tvansteenburgh]

LGTM, thanks @johnsca