Call Python UDF on ArrayType/MapType/PrimitiveType, the returnType can also be ArrayType/MapType/PrimitiveType.

For StructType, it will act as tuple (without attributes). If returnType is StructType, it also should be tuple.

Author: Davies Liu <davies@databricks.com>

Closes #2973 from davies/udf_array and squashes the following commits:

306956e [Davies Liu] Merge branch 'master' of github.com:apache/spark into udf_array
2c00e43 [Davies Liu] fix merge
11395fa [Davies Liu] Merge branch 'master' of github.com:apache/spark into udf_array
9df50a2 [Davies Liu] address comments
79afb4e [Davies Liu] type conversionfor python udf