When opening PR then create a new TR

[atodorov]

When a new pull request is opened on GitHub we should create a new TestRun for it. This can be extended/only if there is a special config/commit log message, reference to a TC or TP.

This can also serve to trigger 3rd party tests (e.g. dependencies) by utilizing the upcoming triggering functionality in the TestRun.

From the POV of initiator we only need to know how to reach Kiwi TCMS and create a test run. The rest will be handled by the server.

Update: when PR statuses are updated (e.g. Travis, Snyk, Scrutinizer) we should somehow add this information back to Kiwi TCMS, see original report in kiwitcms/Kiwi#817