[FLINK-11767] Introduce new TypeSerializerUpgradeTestBase

[tzulitai]

What is the purpose of the change

This PR introduces TypeSerializerUpgradeTestBase to fully replace TypeSerializerSnapshotMigrationTestBase.

The old test base needs to be replaced because it does not provide any means to generate test serializer snapshot files for each corresponding serializer. Before, what was written in the serializer snapshot test files and how they were written was not visible at all to developers, and also caused a lot of trouble when attempting to release new Flink versions and we have to generate new test files for the current version.

As part of this change, the PR introduces a utility class ClassRelocator.
This utility allows us to relocate classes to a different name.
We require this in the serializer upgrade tests, because some test scenarios attempt to test schema upgrades, e.g. adding / removing fields from a Pojo class.
The ClassRelocator utility allows us to define two different versions of a Pojo class under the same name (one pre-upgrade that is used for writing the test serializer snapshot file, and the other after upgrade used for upgrade verification).

Brief change log

• ed1be69 introduces ClassRelocator
• 24f8356 introduces new test base TypeSerializerUpgradeTestBase
• 2bcdaed Adds a new PojoSerializer upgrade test based on the new test base.

Verifying this change

• Run the new PojoSerializerUpgradeTest. It should work also in the IDE.
• All test snapshot files should be auto-generated, if they do not exist.

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 2bcdaed (Tue Nov 26 09:35:38 UTC 2019)

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CI report:

• 2bcdaed Travis: FAILURE
• fdf0407 Travis: SUCCESS Azure: SUCCESS

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[igalshilman]

Hi @tzulitai,
Thanks for working on this, indeed this seems like an important improvement.
I've checked the PR locally and ran PojoSerializerUpgradeTest, I've also used the base class to generate new test files and everything seems to work as expected.

LGTM 👍

[aljoscha]

This currently doesn't compile correctly because we use the wrong shaded ASM7 dependency. I fixed this and also added a couple more commits to add test support for Flink 1.8 and 1.9, once travis is green I'll merge this.

[aljoscha]

I pushed my changes to this PR so that you can have a look.

cc @igalshilman

[tzulitai]

I went over @aljoscha's recent changes, +1 to merge.
Travis also gives green now.
Will proceed to merge this, thanks for the reviews and follow-ups @aljoscha @igalshilman.

[tzulitai]

Manually merged.
master - 9362fc9
release-1.10 - 3c314fc