Local apt defaults

For @howbazaar to correct local environment update/upgrade behavior when bootstrapping.

Running all tests locally now. I won't land unless they pass on my machine, but I wanted to get this up for review.
I think we need a check that mcfg.EnableOSUpgrade matches what we expect - based on what's in environ config. You may need to use a factory method to return mockFinish based on passed in expected values for EnableOSRefreshUpdate and EnableOSUpgrade