Need to detect if zero nova-consoleauths are enabled

[Drew Freiberger]

In a new 18.11 charms deployment, it was identified that there is a bug lp#1805658 that caused nova-consoleauth startup failures on all nodes of the cluster. This was not detected by monitoring, and took several days to troubleshoot why consoles weren't working. A simple addition to the nova services checks would be to ensure that at least one nova-consoleauth is in enabled/up state.

Stretch goal, find a way to related to nova-cloud-controller to receive the single-nova-consoleauth attribute and if set to "false" check for $num_nova-consoleauth_enabled == $num_nova-cloud-controller_units.

[Xav Paice (xavpaice)]

First step for fixing this is to evaluate if this check should actually be in the nova-cloud-controller charm or in openstack-service-checks, and if it's still relevant for the newest versions.