State: Add EnvUUID to Network docs

Add three upgrade steps. The first two prepend the envuuid to the _id of networks and requestedNetworks doc as well as add a env-uuid field. The third step only adds the env-uuid field to the networkInterfaces doc.

Update helper functions in state/upgrades_test.go to support optionally add only the env-uuid field, leaving the original _id value.
Merge branch 'master' of https://github.com/juju/juju into migrate-network
Merge pull request #1109 from waigani/migrate-network

State Upgrade Step: Add EnvUUID to Network docs

Add three upgrade steps. The first two prepend the envuuid to the _id of networks and requestedNetworks doc as well as add a env-uuid field. The third step only adds the env-uuid field to the networkInterfaces doc.

Update helper functions in state/upgrades_test.go to support optionally add only the env-uuid field, leaving the original _id value.