State upgrade steps: migrate statuses, constraints and annotations

Add an ugrade step for each of statuses, constraints and annotation
collections. Each step appends the environment uuid to the _id field
and adds a new env-uuid field.
Merge branch 'master' of https://github.com/juju/juju into migrate-status-constraints-annotations

Conflicts:
	state/megawatcher.go
Merge branch 'master' of https://github.com/juju/juju into migrate-status-constraints-annotations

Conflicts:
	state/megawatcher.go
Merge pull request #1160 from waigani/migrate-status-constraints-annotations

State upgrade steps: Migrate status, constraints and annotations collections

Add three upgrade steps which append the environment uuid to the _id and and a new env-uuid field to each of status, constraints and annotations/

(Review request: https://reviews.vapour.ws/r/471/)