[FLINK-16263][python][tests] Set io.netty.tryReflectionSetAccessible to true for JDK9+

[dianfu]

What is the purpose of the change

This pull request sets io.netty.tryReflectionSetAccessible to true for JDK9+. See https://issues.apache.org/jira/browse/ARROW-5412 for more details.

Brief change log

• Adds -Dio.netty.tryReflectionSetAccessible=true option to the flink-python unit tests

Verifying this change

Tests manually in my local environment.

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 127112a (Tue Feb 25 06:08:56 UTC 2020)

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[hequn8128]

@dianfu Thanks a lot for the quick fix. Looks good to me.
BTW, we may need to add a document for users to add this option when running on the JDK9+ environment. We can create another jira for this. What do you think?

[dianfu]

@hequn8128 Thanks for the review and suggestion. I'm in favor of making it transparent for users, for example, setting this environment variable in the open method of the Arrow operator to be introduced. I will check if this is possible in the Arrow operator PR. If not, we can add a documentation for users.

[hequn8128]

@dianfu Solve this automatically is good. FYI, (ARROW-7223), It seems setting the property won't help, as it's read at static initialization time. I have created a jira(FLINK-16273) for addressing this problem for users.

I will merge this once Travis passed.

[dianfu]

@hequn8128 Thanks for creating the following-up ticket.