[SPARK-20456][PYTHON][FOLLOWUP] Fix timezone-dependent doctests in unix_timestamp and from_unixtime

[HyukjinKwon]

What changes were proposed in this pull request?

This PR proposes to simply ignore the results in examples that are timezone-dependent in unix_timestamp and from_unixtime.

Failed example:
    time_df.select(unix_timestamp('dt', 'yyyy-MM-dd').alias('unix_time')).collect()
Expected:
    [Row(unix_time=1428476400)]
Got:unix_timestamp
    [Row(unix_time=1428418800)]

Failed example:
    time_df.select(from_unixtime('unix_time').alias('ts')).collect()
Expected:
    [Row(ts=u'2015-04-08 00:00:00')]
Got:
    [Row(ts=u'2015-04-08 16:00:00')]

How was this patch tested?

Manually tested and ./run-tests --modules pyspark-sql.

[HyukjinKwon]

cc @ueshin, could you take a look when you have some time?

[SparkQA]

Test build #79500 has finished for PR 18597 at commit 5c5f405.

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

[ueshin]

How about surrounding with SQLConf spark.sql.session.timeZone as America/Los_Angeles ?

[HyukjinKwon]

Sounds good.

[SparkQA]

Test build #79505 has finished for PR 18597 at commit 31fa09b.

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

[ueshin]

LGTM.

[ueshin]

Thanks! merging to master.

[HyukjinKwon]

Thank you @ueshin.