Trying to prevent the grpc setup from being flaky

[antonpirker]

Automatically select a port and not set it by hand also make creating of the channel more stable.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.53%. Comparing base (5147ab9) to head (bde3e15).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@ Coverage Diff @@## master #4233 +/- ##
==========================================
+ Coverage 79.52% 79.53% +0.01% 
==========================================
Files 142 142 Lines 15898 15898 Branches 2721 2721 ==========================================
+ Hits 12643 12645 +2 
Misses 2389 2389 + Partials 866 864 -2 

see 4 files with indirect coverage changes

[antonpirker]

I have now run the tests five times in a row without the grpc tests being flaky, so I guess this works. (the last time another flaky test failed, but it was not grpc)