[FLINK-14562][Connectors/ RabbitMQ]Idle consumer are left behind on closing

[ndeslandes]

What is the purpose of the change

This pull request fix the close() method on the RMQSource class to clean any consumer that was used in it. This is needed to prevent leaving idle consumer of the RabbitMQ cluster

Brief change log

• Use the channel to cancel the active consumer
• Close the channel itself
• Close the connection (was already there)

Verifying this change

The close method does not seem to be tested right now and I am not sure how to add a test for that.
This fix clearly fix that bug for us in all of our environment and I don’t think it can break anything else.

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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Automated Checks

Last check on commit 25e0907 (Wed Dec 04 14:56:16 UTC 2019)

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[knaufk]

LGTM.

[tillrohrmann]

Thanks for creating this PR @ndeslandes. LGTM. Merging this PR.