[SPARK-2615] [SQL] Add Equal Sign "==" Support for HiveQl

Currently, the "==" in HiveQL expression will cause exception thrown, this patch will fix it.

Author: Cheng Hao <hao.cheng@intel.com>

Closes #1522 from chenghao-intel/equal and squashes the following commits:

f62a0ff [Cheng Hao] Add == Support for HiveQl
Graphx example

fix examples

Author: CrazyJvm <crazyjvm@gmail.com>

Closes #1523 from CrazyJvm/graphx-example and squashes the following commits:

663457a [CrazyJvm] outDegrees does not take parameters
7cfff1d [CrazyJvm] fix example for joinVertices