If the value of 'spark.default.parallelism' does not match the number of partitoins in EdgePartition(EdgeRDDImpl),
the following error occurs in ReplicatedVertexView.scala:72;

object GraphTest extends Logging {
  def run[VD: ClassTag, ED: ClassTag](graph: Graph[VD, ED]): VertexRDD[Int] = {
    graph.aggregateMessages(
      ctx => {
        ctx.sendToSrc(1)
        ctx.sendToDst(2)
      },
      _ + _)
  }
}

val g = GraphLoader.edgeListFile(sc, "graph.txt")
val rdd = GraphTest.run(g)

java.lang.IllegalArgumentException: Can't zip RDDs with unequal numbers of partitions
	at org.apache.spark.rdd.ZippedPartitionsBaseRDD.getPartitions(ZippedPartitionsRDD.scala:57)
	at org.apache.spark.rdd.RDD$$anonfun$partitions$2.apply(RDD.scala:206)
	at org.apache.spark.rdd.RDD$$anonfun$partitions$2.apply(RDD.scala:204)
	at scala.Option.getOrElse(Option.scala:120)
	at org.apache.spark.rdd.RDD.partitions(RDD.scala:204)
	at org.apache.spark.rdd.MapPartitionsRDD.getPartitions(MapPartitionsRDD.scala:32)
	at org.apache.spark.rdd.RDD$$anonfun$partitions$2.apply(RDD.scala:206)
	at org.apache.spark.rdd.RDD$$anonfun$partitions$2.apply(RDD.scala:204)
	at scala.Option.getOrElse(Option.scala:120)
	at org.apache.spark.rdd.RDD.partitions(RDD.scala:204)
	at org.apache.spark.ShuffleDependency.<init>(Dependency.scala:82)
	at org.apache.spark.rdd.ShuffledRDD.getDependencies(ShuffledRDD.scala:80)
	at org.apache.spark.rdd.RDD$$anonfun$dependencies$2.apply(RDD.scala:193)
	at org.apache.spark.rdd.RDD$$anonfun$dependencies$2.apply(RDD.scala:191)
    ...

Author: Takeshi Yamamuro <linguin.m.s@gmail.com>

Closes #4136 from maropu/EdgePartitionBugFix and squashes the following commits:

0cd8942 [Ankur Dave] Use more concise getOrElse
aad4a2c [Ankur Dave] Add unit test for non-default number of edge partitions
0a2f32b [Takeshi Yamamuro] Do not use Partitioner.defaultPartitioner as a partitioner of EdgeRDDImpl