fix posting of comment in PR with --upload-test-report

[boegel]

fix for bug that was introduced in recently merged PR #3189 that occurs when --upload-test-report:

Traceback (most recent call last):
  File "/usr/lib64/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib64/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/main.py", line 518, in <module>
    main()
  File "/lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/main.py", line 497, in main
    test_report_msg = overall_test_report(ecs_with_res, len(paths), overall_success, success_msg, init_session_state)
  File "/lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/tools/testing.py", line 313, in overall_test_report
    txt = post_easyconfigs_pr_test_report(pr_nr, test_report, msg, init_session_state, success)
  File "/lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/tools/testing.py", line 289, in post_easyconfigs_pr_test_report
    post_comment_in_issue(pr_nr, comment, account=pr_target_account, repo=pr_target_repo, github_user=github_user)
  File "/lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/tools/github.py", line 554, in post_comment_in_issue
    status, data = pr_url.comments.post(body={'body': txt})
  File "/lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/base/rest.py", line 137, in post
    return self.request(self.POST, url, json.dumps(body), headers, content_type='application/json')
  File "lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/base/rest.py", line 174, in request
    conn = self.get_connection(method, url, body, headers)
  File "/lib/python2.7/site-packages/easybuild_framework-4.2.0.dev0-py2.7.egg/easybuild/base/rest.py", line 215, in get_connection
    connection = self.opener.open(request)
  File "/usr/lib64/python3.6/urllib/request.py", line 532, in open
    response = meth(req, response)
  File "/usr/lib64/python3.6/urllib/request.py", line 642, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib64/python3.6/urllib/request.py", line 570, in error
    return self._call_chain(*args)
  File "/usr/lib64/python3.6/urllib/request.py", line 504, in _call_chain
    result = func(*args)
  File "/usr/lib64/python3.6/urllib/request.py", line 650, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 404: Not Found

The underlying cause was the use of None in the URL composed to post the comment by the post_comment_in_issue function (called by post_easyconfigs_pr_test_report), for example:

== 2020-04-08 19:56:13,905 rest.py:214 DEBUG opening request:  https://api.github.com/repos/easybuilders/None/issues/10354/comments

This occurs because the default value for --pr-target-repo was changed to None in #3189...

[zao]

-u works again with this PR for me.

[zao]

Going in, thanks @boegel!