[SPARK-7832] [Build] Always run SQL tests in master build.

https://issues.apache.org/jira/browse/SPARK-7832

Author: Yin Huai <yhuai@databricks.com>

Closes #6385 from yhuai/runSQLTests and squashes the following commits:

3d399bc [Yin Huai] Always run SQL tests in master build.