State upgrade step: Add EnvUUID to charm docs.

Add an upgrade step to add the environment uuid to charm docs. Update
doc struct, call sites and tests respectively.
fixed conflicts
Merge branch 'master' of https://github.com/juju/juju into migrate-charms

Conflicts:
	upgrades/steps121_test.go
Merge branch 'master' of https://github.com/juju/juju into migrate-charms

Conflicts:
	state/upgrades.go
	state/upgrades_test.go
Merge branch 'master' of https://github.com/juju/juju into migrate-charms
Merge branch 'master' of https://github.com/juju/juju into migrate-charms
Merge branch 'master' of https://github.com/juju/juju into migrate-charms

Conflicts:
	state/upgrades.go
	upgrades/steps121.go
	upgrades/steps121_test.go
Merge pull request #982 from waigani/migrate-charms

State upgrade step: Add EnvUUID to charm docs.

Add an upgrade step to add the environment uuid to charm docs. Update doc struct, call sites and tests.