Prepend EnvUUID to _id of each services doc.

Add an upgrade step, respective tests and a helper function to change
the _id field of each service doc from "id" to "envUUID:id".
Merge branch 'master' of https://github.com/juju/juju into envuuid-serviceid
Merge branch 'master' of https://github.com/juju/juju into envuuid-serviceid
Merge branch 'master' of https://github.com/juju/juju into envuuid-serviceid
Merge pull request #802 from waigani/envuuid-serviceid

Prepend EnvUUID to _id of each services doc.

Add an upgrade step, respective tests and a helper function to change
the _id field of each service doc from "id" to "envUUID:id".