[SPARK-21435][SQL] Empty files should be skipped while write to file

[xuanyuanking]

What changes were proposed in this pull request?

Add EmptyDirectoryWriteTask for empty task while writing files.

How was this patch tested?

Add new test in FileFormatWriterSuite

[HyukjinKwon]

Please refer the discussion in #17395. I am quite sure this is going to break

spark.range(100).filter("id > 100").write.parquet("/tmp/abc")
spark.read.parquet("/tmp/abc").show()

I think we should close and propose another approach in a separate PR.

[SparkQA]

Test build #79661 has finished for PR 18650 at commit ff92ba3.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #79665 has finished for PR 18650 at commit e08fb19.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[xuanyuanking]

Yep, just close this and open #18654