migrations: fix azure AdoptResources

[babbageclunk]

Description of change

Update the resource group controller tag as well as the resources.

Previously it would update all the resources but not the group, which meant the
contained resources will still be killed by an old controller being destroyed.

QA steps

• bootstrap two controllers on Azure, A and B
• add a model on A
• deploy an application the model
• migrate the model to B
• once the migration is complete and the model is running on B, destroy controller A
• the model should continue running on B

Bug reference

Part of fix for https://bugs.launchpad.net/juju/+bug/1648063

[babbageclunk]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju