Add wait_policy option to EmrCreateJobFlowOperator.

[adrian-adikteev]

---

Currently, when using wait_for_complition=True it will trigger the node to only wait until the cluster is successfully launched.
I added the option wait_policy so that one can chose what waiter will be used.

Possible values:

• None: No wait (default)
• WaitPolicy.WAIT_FOR_COMPLETION: Previous behaviour when wait_for_completion was True
• WaitPolicy.WAIT_FOR_STEPS_COMPLETION: New behaviour - wait for the cluster to terminate.

This is useful because it will eliminate the need to have an extra node in your DAG.

[boring-cyborg]

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[vincbeck]

Could you cover this new use case in a unit test?

[vincbeck]

Good job! I like that version

[adrian-adikteev]

I'm not sure what's the next step here but from my side everything is ready.

[vincbeck]

Overall looks good! Just one nit and you do not a newsfragment for this change

[vincbeck]

Perfect!

[adrian-adikteev]

Should be ready for merge

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.