Improvements to autoscaler to automatically re-attempt fail pull [pending patch]

[bradrydzewski]

@trondhindenes

It would seem to me that any piece of code that deals with spinning up vms, waiting for them to be connect-able etc needs very robust retrying because so many things can happen that is outside the control of the system.

The system does retry to connect to the daemon before running a docker pull. You can analyze the retry logic here: https://github.com/drone/autoscaler/blob/master/engine/install.go#L117:L141