improve GetCluster message when Subscription exists but is inactive

[cben]

First step towards #517.
At least doesn't lie to user and gives hint how to find past data:

before

> ocm describe cluster 0e68a621-c00e-4bbf-a4bb-9915ae6cc947
Error: Can't retrieve cluster for key '0e68a621-c00e-4bbf-a4bb-9915ae6cc947': There are no subscriptions or clusters with identifier or name '0e68a621-c00e-4bbf-a4bb-9915ae6cc947'

after

> ocm describe cluster 0e68a621-c00e-4bbf-a4bb-9915ae6cc947
Error: Can't retrieve cluster for key '0e68a621-c00e-4bbf-a4bb-9915ae6cc947': Cluster was Deprovisioned, see `ocm get subscription 2S434jffVG4fSgDdK4cbkDTxVNp` for details``

This affects ALL commands that use GetCluster helper.

❓ Behavior change: when there is 1 active cluster and also 1+ past clusters reusing same display_name, previously the active one was silently used; now will refuse treating them as ambiguous:

> ocm get subs -p search="display_name in ('servheredia')" | jq .items[].status | sort | uniq -c
      4 "Deprovisioned"
      1 "Reserved"
> ocm describe cluster servheredia
Error: Can't retrieve cluster for key 'servheredia': There are 5 subscriptions with cluster identifier or name 'servheredia'

is that desired?

[mjlshen]

I'm curious about this change:

❓ Behavior change: when there is 1 active cluster and also 1+ past clusters reusing same display_name, previously the active one was silently used; now will refuse treating them as ambiguous:

The behavior of ocm describe cluster to just show the active cluster was desired by me. When I spin up a test cluster I tend to keep the same name, so now when I want to us ocm describe cluster I would have to use one of the IDs instead which are unpredictable.

I appreciate that we want a way to query archived clusters with ocm cli - but is there a flag we can add to keep the old behavior, maybe --active? Alternatively, the opposite and keeping the old behavior by default and adding a --archives?

[cben]

When I spin up a test cluster I tend to keep the same name

Good point. I'm less involved with ocm-cli now so I'm not the right person to decide this. I recommend opening a new issue.

[cben]

Or bring this up on #517. One of the open questions there was that many commands using GetCluster() only make sense on Active clusters...
(This PR was not so much a solution as provocation to explore the question 😉)