get strings from omero.cmd.ERR and omero.CmdError correctly

[will-moore]

Fixes #481

This fixes 2 similar bugs where we're handling omero.CmdError or omero.cmd.ERR objects and converting into strings.

Both were previously failing with AttributeError: 'ERR' object has no attribute 'message'.

Changes based on using the appropriate attributes as tested at #481 (comment)

[sbesson]

The usage of str(omero.CmdError) matches the intent of this API introduced in ome/omero-py#151

For the omero.cmd.ERR handling, as an element of comparison the CLI implementation in https://github.com/ome/omero-py/blob/0dc60bd67a5f9281e2063a0a3aeeaa119c14447d/src/omero/cli.py#L1907-L1927 uses rsp.name as the error message and rsp.parameters as the report. Would it make sense to align the behavior in OMERO.web

[will-moore]

I tried str(err) for both cases at #481 (comment) and it gave sub-optimal results.
Not sure exactly what the difference is between omero.CmdError and omero.cmd.ERR!

[will-moore]

@sbesson updated as suggested to use str(omero.CmdError) and str(omero.cmd.ERR.name)

[will-moore]

cc @knabar This is not an urgent PR, but it is a trivial fix so could maybe get reviewed and included in the next release?

[sbesson]

@will-moore I have not had a chance to get back to those. For both updates, do you have scenarios that would allow to reproduce the original errors and asses the impact of the changes functionally?

[will-moore]

@sbesson No, unfortunately I don't have scenarios to reproduce those errors. We only have stack traces from QA, but don't know what caused them (difficult to understand from the stack traces themselves).
I could try guessing a few, but not sure where to start

[knabar]

@will-moore I'm curious if these missing attributes existed in the past, and if so, when they were removed or renamed. Discussed with @sbesson a bit and he pointed out this could be related to Python 2/3 upgrades as well.

Overall I feel we need a bit more investigation, so I'd like to hold off on this one until 5.26.0, which could come fairly soon anyway.

[will-moore]

@knabar I don't think they've ever existed. It was just assumed that an exception would have a message attribute.