Make tests on delete_job skippable

[diego-plan9]

Summary

Tweak the reintroduced delete_job tests (from #2541) so they are skipped in case the credentials do not allow for deletion of jobs.

Details and comments

Fixes #2548

[yaelbh]

1. Can we not skip if the error is 1401?
2. Can we know in advance if there are privileges, to refrain from running the program?
3. It will be good to ask Matt to approve as well, as the creator of the issue.

[diego-plan9]

CC @mriedem indeed for review and the above questions.

[yaelbh]

@diego-plan9 The first question is in fact a code review comment. It amounts to refining "403" in ex.message to verify that the characters before and after 403 are not number, and the same also for 401.

[diego-plan9]

Ah, I misread and thought you were asking to avoid skipping if the HTTP error was 401. I pushed f9e1f2f with a less ambiguous matching: unfortunately, the real RequestsApiError exception does not get raised from the IBMRuntimeError so we are limited to comparing the strings, but hopefully this will indeed prevent it picking up other strings unintendedly.