[FLINK-13759][builds] Fix builds for master branch are failed during compile stage

[wuchong]

What is the purpose of the change

Fix builds for master branch are failed during compile stage.

Brief change log

• flink-connector-elasticsearch doesn't exist at all. Fix the travis script to check flink-connector-elasticsearch6.

Verifying this change

This change is a trivial work without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Automated Checks

Last check on commit 23a72b2 (Fri Aug 23 10:22:10 UTC 2019)

Warnings:

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CI report:

• 23a72b2 : SUCCESS Build

[tillrohrmann]

Thanks a lot for fixing this problem so quickly @wuchong. LGTM. Merging.

Do you know why the build passed until a couple of days ago? I thought we removed the old elastic search connector quite some time ago and it should have failed right away. Maybe @zentol can help with that as well.

[wuchong]

I have the same question. It should fail for a long time ago. Could this because of Travis caching mechanism?

[tillrohrmann]

The reason why the build failed was indeed a cache inconsistency and not check_shaded_artifacts_connector_elasticsearch which checked for a non-existing connector directory. @zentol could it be that check_shaded_artifacts_connector_elasticsearch does not properly fail the build if it cannot find a directory?

[zentol]

Based on the JIRA error the check does fail if the directory or file doesn't exist.

I would conclude that the directory did exist, but as far as I can tell there shouldn't be a way for the cache to contain old date; Flink should always be compiled in a clean directory which is then cached separately from other builds.