[FLINK-18063][checkpointing] Fix the race condition for aborting current checkpoint in CheckpointBarrierUnaligner

[zhijiangW]

What is the purpose of the change

There are three aborting scenarios which might encounter race condition:

1. CheckpointBarrierUnaligner#processCancellationBarrier
2. CheckpointBarrierUnaligner#processEndOfPartition
3. AlternatingCheckpointBarrierHandler#processBarrier

They only consider the pending checkpoint triggered by #processBarrier from task thread to abort it. Actually the checkpoint might also be triggered by #notifyBarrierReceived from netty thread in race condition, so we should also handle properly to abort it.

Brief change log

• Fix the process of AlternatingCheckpointBarrierHandler#processBarrier
• Fix the process of CheckpointBarrierUnaligner#processEndOfPartition to abort checkpoint properly
• Fix the process of CheckpointBarrierUnaligner#processCancellationBarrier to abort checkpoint properly

Verifying this change

• Added new unit test CheckpointBarrierUnalignerTest#testProcessCancellationBarrierAfterNotifyBarrierReceived
• Added new unit test CheckpointBarrierUnalignerTest#testProcessCancellationBarrierAfterProcessBarrier
• Added new unit test CheckpointBarrierUnalignerTest#testProcessCancellationBarrierBeforeProcessAndReceiveBarrier

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, Kubernetes/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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Last check on commit 72fc053 (Sun Jun 07 14:09:43 UTC 2020)

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[zhijiangW]

Cherry-pick it to master from #12406 which was reviewed and approved before.
The failure e2e is known StreamingKafkaITCase, so ignore it to merge.