[SPARK-19706][PYSPARK] add Column.contains in pyspark

## What changes were proposed in this pull request?

to be consistent with the scala API, we should also add `contains` to `Column` in pyspark.

## How was this patch tested?

updated unit test

Author: Wenchen Fan <[email protected]>

Closes apache#17036 from cloud-fan/pyspark.

Author: cloud-fan

python/pyspark/sql/column.py

@@ -248,6 +248,7 @@ def __iter__(self):
         raise TypeError("Column is not iterable")
 
     # string methods
+    contains = _bin_op("contains")
     rlike = _bin_op("rlike")
     like = _bin_op("like")
     startswith = _bin_op("startsWith")

python/pyspark/sql/tests.py

@@ -944,7 +944,8 @@ def test_column_operators(self):
         self.assertTrue(all(isinstance(c, Column) for c in cb))
         cbool = (ci & ci), (ci | ci), (~ci)
         self.assertTrue(all(isinstance(c, Column) for c in cbool))
-        css = cs.like('a'), cs.rlike('a'), cs.asc(), cs.desc(), cs.startswith('a'), cs.endswith('a')
+        css = cs.contains('a'), cs.like('a'), cs.rlike('a'), cs.asc(), cs.desc(),\
+            cs.startswith('a'), cs.endswith('a')
         self.assertTrue(all(isinstance(c, Column) for c in css))
         self.assertTrue(isinstance(ci.cast(LongType()), Column))