reportportal: upload all test case results

[kkaarreell]

• Upload all test results for a given test case, not just the first one.
• Store guest name and role as test case attributes.
• Rename get_rp_api() to rp_api_get()
• Add and use rp_api_post() and rp_api_put()

Fixes issue #3129

Pull Request Checklist

• [ ] implement the feature
• [ ] write the documentation
• [ ] extend the test coverage
• [ ] update the specification
• [ ] adjust plugin docstring
• [ ] modify the json schema
• [ ] mention the version
• [ ] include a release note