We can simple treat cross join as inner join without join conditions.

Author: Daoyuan Wang <daoyuan.wang@intel.com>
Author: adrian-wang <daoyuanwong@gmail.com>

Closes #2124 from adrian-wang/crossjoin and squashes the following commits:

8c9b7c5 [Daoyuan Wang] add a test
7d47bbb [adrian-wang] add cross join support for hql