Addressing issue in MimaBuild.scala.

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

Closes #742 from jegonzal/edge_partition_serialization and squashes the following commits:

8ba6e0d [Ankur Dave] Add concatenation operators to MimaBuild.scala
cb2ed3a [Joseph E. Gonzalez] addressing missing exclusion in MimaBuild.scala
5d27824 [Ankur Dave] Disable reference tracking to fix serialization test
c0a9ae5 [Ankur Dave] Add failing test for EdgePartition Kryo serialization
a4a3faa [Joseph E. Gonzalez] Making EdgePartition serializable.