[SPARK-8686][SQL] DataFrame should support where with expression represented by String

[sarutak]

DataFrame supports filter function with two types of argument, Column and String. But where doesn't.

[SparkQA]

Test build #35914 has finished for PR 7063 at commit 180f9a4.

• This patch fails some tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class Module(object):

[sarutak]

This failure was due to a bug in dev/run-test.py and it's been already resolved.

Jenkins, retest this please.

[sarutak]

retest this please.

[SparkQA]

Test build #35917 has finished for PR 7063 at commit 180f9a4.

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

[davies]

LGTM, could you also add Python API for it?

[sarutak]

@davies Thanks for taking a look at this. I think, Python API already has right?

[davies]

Got it, merging this into master, thanks!