[bugfix] Fix handling of single character scheduler backend options passed through -J

[rsarm]

closes #1693

[rsarm]

@jenkins-cscs retry dom

[vkarak]

@rsarm I tested the PR and I verified what I pointed out in the issue passing -A=foo is wrong. It's not correct under POSIX and -correctly- Slurm rejects it:

[reframer060@reframe ~]$ srun -ptotal -A reframers hostname
reframe-1
[reframer060@reframe ~]$ srun -ptotal -A=reframers hostname
srun: error: Unable to allocate resources: Invalid account or account/partition combination specified

Should we then treat the -J A=foo option specially and pass -Afoo or -A foo?

[rsarm]

@vkarak oh sorry! I was convinced that -A=foo worked!

I would prefer to do not support translating non-valid options like -A=foo to valid ones. I would expect the user to pass options exactly as they would be set on the scheduler script. On the other hand it's very simple to support it, I guess we can do this

        for opt in options.job_options:
            optstr, valstr = re.split(r'=|\s+', opt, maxsplit=1)
            if opt.startswith('-') or opt.startswith('#'):
                parsed_job_options.append(opt)
            elif len(optstr) == 1:
                parsed_job_options.append(f'-{optstr} {valstr}')
            else:
                parsed_job_options.append(f'--{optstr} {valstr}')

[vkarak]

What I'm proposing I think it's on the same line with the conversion from -J account=foo to --account=foo. To me it seems valid to have a conversion such as -J A=foo to -A foo. The lhs is our syntax. Otherwise, the user would have to quote the argument -J 'A foo' which is not consistent with the account=foo and also not so nice to write. I would vote for supporting just this syntax then.

[vkarak]

lgtm