[SPARK-2823][GraphX]fix GraphX EdgeRDD zipPartitions

If the users set “spark.default.parallelism” and the value is different with the EdgeRDD partition number, GraphX jobs will throw:
java.lang.IllegalArgumentException: Can't zip RDDs with unequal numbers of partitions

Author: luluorta <luluorta@gmail.com>

Closes #1763 from luluorta/fix-graph-zip and squashes the following commits:

8338961 [luluorta] fix GraphX EdgeRDD zipPartitions

(cherry picked from commit 9b225ac3072de522b40b46aba6df1f1c231f13ef)
Signed-off-by: Ankur Dave <ankurdave@gmail.com>