migrations: machine sanity check fails on Azure

[Christian Muirhead]

When migrating a model from one Azure controller to another, the sanity check fails because there's an instance named 'common' that doesn't correspond to a machine in the model.

2017-08-23 06:13:10 INFO juju.worker.migrationmaster.0712d2 worker.go:275 checking machines in migrated model
2017-08-23 06:13:11 ERROR juju.worker.migrationmaster.0712d2 worker.go:472 no machine with instance "common"
2017-08-23 06:13:11 ERROR juju.worker.migrationmaster.0712d2 worker.go:279 machine sanity check failed, 1 error found
2017-08-23 06:13:11 INFO juju.worker.migrationmaster.0712d2 worker.go:249 setting migration phase to ABORT
2017-08-23 06:13:11 INFO juju.worker.migrationmaster.0712d2 worker.go:275 aborted, removing model from target controller

Not sure where the common instance is coming from, probably it just needs to be in an allow-list.

[Andrew Wilkins (axwalk)]

https://github.com/juju/juju/pull/7798

[Anastasia (anastasia-macmood)]

I suspect that the fix for this has been already ported into 2.3 (develop) as part of one of the larger merges we have undertaken recently.