contrail-openstack should notify if api servers list is empty

[gmeszaros]

In a scenario when the contrail API servers list could not be queried from the relations, the contrail-openstack charm renders an empty list in the ContrailPlugin.ini.

https://github.com/tungstenfabric/tf-charms/blob/master/contrail-openstack/hooks/contrail_openstack_utils.py#L252

should not return list(), but set juju status to blocked and claim that a mandatory relation data is missing (and maybe should remove and add the contrail-controller relation)

[jhobbs]

"In a scenario when the contrail API servers list could not be queried from the relations" What scenario is this? Was the relation never added or was there some other problem?

[gmeszaros]

I've deployed it through a full bundle, so the relations are there definitely. The controller_ips config was empty for some reason, I don't remember now for sure, but there was some bug around how the templates got rendered. And that has led to this issue. Obviously if the bug weren't there, this bug would not be open.