SPARK-1770: Load balance elements when repartitioning.

This patch adds better balancing when performing a repartition of an
RDD. Previously the elements in the RDD were hash partitioned, meaning
if the RDD was skewed certain partitions would end up being very large.

This commit adds load balancing of elements across the repartitioned
RDD splits. The load balancing is not perfect: a given output partition
can have up to N more elements than the average if there are N input
partitions. However, some randomization is used to minimize the
probabiliy that this happens.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #727 from pwendell/load-balance and squashes the following commits:

f9da752 [Patrick Wendell] Response to Matei's feedback
acfa46a [Patrick Wendell] SPARK-1770: Load balance elements when repartitioning.
SPARK-1652: Set driver memory correctly in spark-submit.

The previous check didn't account for the fact that the default
deploy mode is "client" unless otherwise specified. Also, this
sets the more narrowly defined SPARK_DRIVER_MEMORY instead of setting
SPARK_MEM.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #730 from pwendell/spark-submit and squashes the following commits:

430b98f [Patrick Wendell] Feedback from Aaron
e788edf [Patrick Wendell] Changes based on Aaron's feedback
f508146 [Patrick Wendell] SPARK-1652: Set driver memory correctly in spark-submit.
Fix error in 2d Graph Partitioner

Their was a minor bug in which negative partition ids could be generated when constructing a 2D partitioning of a graph.  This could lead to an inefficient 2D partition for large vertex id values.

Author: Joseph E. Gonzalez <joseph.e.gonzalez@gmail.com>

Closes #709 from jegonzal/fix_2d_partitioning and squashes the following commits:

937c562 [Joseph E. Gonzalez] fixing bug in 2d partitioning algorithm where negative partition ids could be generated.
SPARK-1786: Edge Partition Serialization

This appears to address the issue with edge partition serialization.  The solution appears to be just registering the `PrimitiveKeyOpenHashMap`.  However I noticed that we appear to have forked that code in GraphX but retained the same name (which is confusing).  I also renamed our local copy to `GraphXPrimitiveKeyOpenHashMap`.  We should consider dropping that and using the one in Spark if possible.

Author: Ankur Dave <ankurdave@gmail.com>
Author: Joseph E. Gonzalez <joseph.e.gonzalez@gmail.com>

Closes #724 from jegonzal/edge_partition_serialization and squashes the following commits:

b0a525a [Ankur Dave] Disable reference tracking to fix serialization test
bb7f548 [Ankur Dave] Add failing test for EdgePartition Kryo serialization
67dac22 [Joseph E. Gonzalez] Making EdgePartition serializable.