HOTFIX: Clean up build in network module.

This does a few things
- Uses consistent artifact naming
- Changes this to use scalatest
- Adds this to sbt

One thing to note, it turns out that scalatest when invoked in the
Maven build doesn't succesfully detect JUnit Java tests. This is
a long standing issue, I noticed it applies to all of our current
test suites as well. I've created SPARK-4159 to fix this.