[BEAM-3573] Move GCPIO test utilities to main jar

[kennknowles]

These test utilities are used by clients to test their code. They are not isolated to the test suite jar.

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---	---	---	---	---
Java
Python		---			---	---	---

[kennknowles]

There is some hope that eliminating bad test jar deps might mitigate https://issues.apache.org/jira/browse/BEAM-5035, https://issues.apache.org/jira/browse/BEAM-5207, https://issues.apache.org/jira/browse/BEAM-5116. In any case it is the right direction so no harm in moving to find out how much it helps.

[kennknowles]

R: @apilloud

I believe you did the deepest digging on this parallel build issue. From the issues and gists, I'm not 100% certain it all comes back to this, but I'm not 100% certain it doesn't. Our other modules have test deps that can be just "test runtime" deps. But I'm pretty sure this is the only hard dependency on a class in another test jar for any transitive dep of the tasks I saw failing.

[apilloud]

I did little to no digging beyond disabling parallel tests to fix flakes. This looks like it might fix the root cause. LGTM.

[kennknowles]

run java postcommit

[kennknowles]

The failure in postcommit is the same from #6864. We have tests in the Dataflow worker codebase that are not thread safe. I will drop that commit, then this should be g2g.

[kennknowles]

run java postcommit