[SPARK-2386] [SQL] RowWriteSupport should use the exact types to cast.

When execute `saveAsParquetFile` with non-primitive type, `RowWriteSupport` uses wrong type `Int` for `ByteType` and `ShortType`.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1315 from ueshin/issues/SPARK-2386 and squashes the following commits:

20d89ec [Takuya UESHIN] Use None instead of null.
bd88741 [Takuya UESHIN] Add a test.
323d1d2 [Takuya UESHIN] Modify RowWriteSupport to use the exact types to cast.