[SPARK-8362] [SQL] Add unit tests for +, -, *, /, %

Added unit tests for all supported data types for:
- Add
- Subtract
- Multiply
- Divide
- UnaryMinus
- Remainder

Fixed bugs caught by the unit tests.

Author: Reynold Xin <rxin@databricks.com>

Closes #6813 from rxin/SPARK-8362 and squashes the following commits:

fb3fe62 [Reynold Xin] Added Remainder.
3b266ba [Reynold Xin] [SPARK-8362] Add unit tests for +, -, *, /.