retries hide legitimate errors in Model.connect()

[samuelallan72]

I had an issue with cou hanging on connect. I removed the retry logic and then it crashed with this error:

juju.errors.JujuConnectionError: juju server-version 3.4.2 not supported

We shouldn't retry on these kind of hard errors.

[samuelallan72]

Note a concrete example is that currently running cou plan with a model deployed with an incompatible juju version results in a generic connection error:

$ cou plan
Full execution log: '/home/ubuntu/.local/share/cou/log/cou-20240625053441.log'
Connecting to 'admin/openstack' model... ✖
The connection was lost. Check your connection or increase the timeout.

But removing the retry logic results in a more useful error like:

2024-06-25 05:35:21 [ERROR] Error occurred in Juju's Python library.
2024-06-25 05:35:21 [ERROR] juju server-version 3.4.2 not supported

Perhaps this is a separate issue, but cou really should output a better error when running against an incompatible juju version.