Support for more comprehensive harvesting mode vs binary safe-mode.
Changes after round 1 of reviews.
Merge branch 'master' into lp-1345553-harvest

Conflicts:
	environs/config/config.go
	worker/provisioner/provisioner_task.go
	worker/provisioner/provisioner_test.go
Merge branch 'master' into lp-1345553-harvest
Fixes from review.
Merge pull request #630 from katco-/lp-1345553-harvest

Support for more comprehensive harvesting mode vs binary safe-mode.

https://bugs.launchpad.net/juju-core/+bug/1345553