[FLINK-16877][table-runtime] SingleDirectoryWriter should not produce file when no input record

[JingsongLi]

What is the purpose of the change

SingleDirectoryWriter should not produce file when no input record.
Now it will produce an empty file, we should avoid this.

Brief change log

Modify SingleDirectoryWriter to lazy creating OutputFormat.

Verifying this change

PartitionWriterTest.testEmptySingleDirectoryWriter

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)

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Last check on commit 31914ab (Tue Mar 31 07:02:24 UTC 2020)

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[leonardBang]

Thanks @JingsongLi for contribution, +1 to merge.

[JingsongLi]

Thanks @leonardBang for the review. Merging...