Vaadin Flow pull requests validation improvements

[mshabarov]

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Describe your motivation

Flow team would like to propose the following improvement to Flow PR validation process:

1. Cherry pick pull requests sometimes stuck because of “waiting for status to be reported” for Formatter , Gradle Tests , Sonar (I listed it from memory but probably there was a Validation instead of Sonar), so each time it happens we open Team City “Flow Pull Requests Validation set” and start the builds manually. Do you know how to avoid this?

2. Sometimes flaky tests fail the validation. When I restart the failed test in “Actions” tab, I always end up with the message:

Starting download for saved-workspace
Error: Unable to find an artifact with the name: saved-workspace

and need to restart all the jobs then. There was a discussion about that: there should be a way how to store artifacts between restarts to make the restart working.

3. Cherry-picks had been merged automatically (if no conflicts), but it stopped working at some point. Nowadays it needs a manual approval. Do you know what was changed?