[FLINK-17424][e2e] Further stabilize Elasticsearch in test_sql_client.sh

[twalthr]

What is the purpose of the change

Another attempt to improve the error rate when downloading Elasticsearch. If this doesn't help, we need to put a loop around curl and retry ourselves. There is a --retry-all-errors but this is not available on all machines yet.

Brief change log

• Continue download at last position if possible.
• Use OSS version

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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 a7c9e34 (Tue Nov 24 13:59:19 UTC 2020)

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[twalthr]

I just found out that there is a no JDK version as well. It could further shorten the download time.

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CI report:

• bc32b71 UNKNOWN
• fd91c2a Azure: SUCCESS

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[aljoscha]

Why's the http version more stable than https?

[twalthr]

80% of all errors are TLS errors, we don't necessarily need TLS if it makes the downloads more stable

[aljoscha]

Thanks! This PR should be good to go then.