[FLINK-14434][coordination] Dispatcher#createJobManagerRunner returns on creation succeed

[tisonkun]

What is the purpose of the change

Fixes a race condition described detailedly in FLINK-14434.

Brief change log

Let Dispatcher#createJobManagerRunner returns on creation succeed.

Verifying this change

I think this change is straightforward and current behavior doesn't break guarded by existing tests. The diff attached on corresponding JIRA can reproduce the issue but I'm afraid it is always invasive to emulate this case(add a debug latch between jobManagerRunner.start and return for testing hook in my mind). Due to the change is straightforward and easy to reason, I tend to avoid invasive testing hook.

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, 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 baacecb (Thu Oct 24 18:02:28 UTC 2019)

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[tillrohrmann]

Thanks for this PR @tisonkun. I had a comment concerning the semantics we would change with this PR and a potential idea for solving this and the original problem.

[tillrohrmann]

The change is good. Merging it now. Thanks a lot for providing this fix @tisonkun.

[tisonkun]

Thanks for your review Till!