[FLINK-7311][tests] refrain from using fail(Exception#getMessage())

[NicoK]

What is the purpose of the change

Refrain from using fail(Exception#getMessage()) because it hides the exception's stack trace and is bad style.

This PR is based on #4445.

Brief change log

• remove code pattern fail(Exception#getMessage()) and let the tests throw exceptions instead

Verifying this change

This change is a trivial rework / code cleanup without any new 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, Yarn/Mesos, ZooKeeper: (no)

Documentation

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

[zentol]

I will review this in the evening.

[zentol]

+1.

5 minutes well spent.

[NicoK]

actually, the FLINK-7311 commit also cleanly applies to master (without FLINK-7310 that this PR is based on). Should I rebase?

[zentol]

If FLINK-7310 also cleanly applies to FLINK-7311 as well, i would say yes. If not it's up to you whether you want to invest the time for a rebase.

[zentol]

merging.