[FLINK-17332][k8s] Fix restart policy not equals to Never for native task manager pods

[zhengcanbin]

What is the purpose of the change

Currently, we do not explicitly set the RestartPolicy for the task manager pods in the native K8s setups so that it is Always by default. From the K8s RM perspective, the task manager pod itself must not restart the failed Container, the decision for how to deal with the failed task manager pod must always be made by the active job manager.

Therefore, this PR proposes to set the RestartPolicy to Never for the task manager pods.

Brief change log

• Set Pod.Spec.RestartPolicy to Never in InitTaskManagerDecorator#decorateFlinkPod

Verifying this change

This change added a new unit test:

• InitTaskManagerDecoratorTest#testRestartPolicy

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 95dba08 (Thu Apr 30 01:56:00 UTC 2020)

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[zhengcanbin]

cc @tisonkun. Could you help review this PR? Thanks a lot!

[tisonkun]

Thanks for your contribution @zhengcanbin ! LGTM. Merging...