IS-IS Interface missing when interface is down

[mngan]

This is more of an issue related to eapi's implementation rather than pyeapi specifically.

When you execute show isis interface detail, any IS-IS interface that is operationally down is completely missing from the output of this command. I would expect that the interface would still be present, but have adjacency counts of zero. We are trying to use this for alerting when we lose adjacencies, but this is a lot harder when there isn't a simple gauge we can monitor. Instead we have to detect when an interface disappears from the list of IS-IS interfaces but that could be caused by a lot of other things.

In comparison, looking at the OpenConfig/NetCONF data that gets returned, the downed interface does show up, but is missing the circuit counters block. This is better since we still have a record of all the IS-IS interfaces, and we can just default all the circuit counter values to zero.