[SPARK-12744] [SQL] Change parsing JSON integers to timestamps to treat integers as number of seconds

[antlypls]

JIRA: https://issues.apache.org/jira/browse/SPARK-12744

This PR makes parsing JSON integers to timestamps consistent with casting behavior.

[antlypls]

cc @yhuai

[yhuai]

ok to test

[yhuai]

How about we use

withTempTable("jsonTable") {
  ... the test ...
}

withTempTable can automatically drop the temp table.

[yhuai]

@antlypls Thank you for the PR! Overall it looks good. Just left two comments about the test.

[SparkQA]

Test build #49086 has finished for PR 10687 at commit 2c79bef.

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

[antlypls]

@yhuai I've updated test according to your comments, not sure why build failed.

[JoshRosen]

Jenkins, retest this please.

[SparkQA]

Test build #49108 has finished for PR 10687 at commit 600f73f.

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

[SparkQA]

Test build #49118 has finished for PR 10687 at commit 600f73f.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[yhuai]

LGTM. Merging to master.