[FLINK-15771][FLINK-16583][tests] Fix issues around SQLClientKafkaITCase

[twalthr]

What is the purpose of the change

This fixes a couple of issues related to the SQL Client and the SQLClientKafkaITCase.

In particular, it fixes a classloading bug that was introduced in the last release while updating the code for the new Pipeline abstractions,

Brief change log

See commit messages.

Verifying this change

This change is already covered by existing tests, such as SQLClientKafkaITCase.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Last check on commit 931d3a2 (Wed Mar 18 11:50:30 UTC 2020)

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[wuchong]

Thanks @twalthr , looks good to me.

[twalthr]

Thanks will merge this and backport it to 1.10 if necessary.

[twalthr]

@wuchong correct me if I'm wrong, but I don't think this fix is necessary for 1.10. The test has been merged for 1.11 and the createPipeline is implemented differently in 1.10.

[wuchong]

I think so. SQLClientKafkaITCase is migrated from test_sql_client_kafka.sh bash script since 1.11. We didn't spot any failures of test_sql_client_kafka.sh in 1.10. We can fix that for 1.10 when we find such error in the future.