Multiple fixes for new backend

[dylanmcreynolds]

Some small fixes for issues found testing against the new backend:

• The new backend reports errors directly in the message body, while the old backed used an "err" object in the json.
• The new backend reports status and errors differently from the old backend, this accommodates those changes. One major change is that there was an inconsistency in reporting 404. Because of this, @jl-wynen added a mechanism in the client code to specify that operations not throw errors if the return is a 404. This PR removes that because as far as I can tell, the new backend only reports 404s when the URL path is bad, in which case throwing a ScicatCommError is desirable.

[jl-wynen]

👍 on simplifying this

[jl-wynen]

You missed the error handling here

pyscicat/pyscicat/client.py

Line 828 in f321072

f'Error retrieving token for user: {err["name"]}, {err["statusCode"]}: {err["message"]}'

and here

pyscicat/pyscicat/client.py

Line 851 in f321072

f' Failed log in: {err["name"]}, {err["statusCode"]}: {err["message"]}'

Also, I noticed that Client._log_in_via_auth_msad doesn't return anything, this is probably on me. Is this method still used by anyone?

[dylanmcreynolds]

Thanks for the catch. I just pushed a commit for that.

I don't know if anyone uses that method, but the server supports the endpoint, so I think we have to leave it in.