[SPARK-11279][PYSPARK] Add DataFrame#toDF in PySpark

Author: Jeff Zhang <zjffdu@apache.org>

Closes #9248 from zjffdu/SPARK-11279.

python/pyspark/sql/dataframe.py

@@ -1266,6 +1266,18 @@ class DataFrame(object):
             raise TypeError("col should be a string or a Column")
         return DataFrame(jdf, self.sql_ctx)
 
+    @ignore_unicode_prefix
+    def toDF(self, *cols):
+        """Returns a new class:`DataFrame` that with new specified column names
+
+        :param cols: list of new column names (string)
+
+        >>> df.toDF('f1', 'f2').collect()
+        [Row(f1=2, f2=u'Alice'), Row(f1=5, f2=u'Bob')]
+        """
+        jdf = self._jdf.toDF(self._jseq(cols))
+        return DataFrame(jdf, self.sql_ctx)
+
     @since(1.3)
     def toPandas(self):
         """Returns the contents of this :class:`DataFrame` as Pandas ``pandas.DataFrame``.