Tuesday evening handover

[Dave Cheney]

Howdy,

Support for the Provisioning agent to start and stop machines landed today. There are some followup branches to land to address some edge cases like machines being removed from behind the PA's back, and enhancements to dummy to improve testability, but right now the PA should be in a position to start making instances.

Out for review
* cmd/jujud: provisioner shuts down unknown instances: https://codereview.appspot.com/6315043
* cmd/jujud: add retry strategy: https://codereview.appspot.com/6295067/

In progress
* environs/dummy: add Instances to Operation results (will find a better way to do this)

Cheers

Dave