State: Migrate instanceId

Add an upgrade step to migrate the depricated "instanceid" machine
field into "instanceid" in the instanceData doc.
fix conflicts
State upgrade step: Add EnvUUID to cleanup docs.

Add an upgrade step which stringifies the cleanup doc (bson.ObjectId)
and prepends State's environment UUID. Update state.docID() to take an
interface and return a string.
Add a --download option to "juju backups create".
Add a --filename option.
Drop superfluous if statement.
Use a more meaningful (in help) "default" for --filename.
Add a recommendation to download backups.
Fix tests.
fix conflicts
Merge branch 'master' of https://github.com/juju/juju into migrate-instanceid
Merge pull request #994 from waigani/migrate-cleanup

State upgrade step: Add EnvUUID to cleanup docs.

Add an upgrade step which stringifies the cleanup doc (bson.ObjectId)
and prepends State's environment UUID. Update state.docID() to take an
interface and return a string.
Merge pull request #1002 from ericsnowcurrently/backups-create-download

Add --download and --filename options to "juju backups create".
Merge pull request #916 from waigani/migrate-instanceid

State: Migrate instanceId

Add an upgrade step to migrate the depricated "instanceid" machine
field into "instanceid" in the instanceData doc.