HOTFIX: Clean up build in network module.

[pwendell]

This is currently breaking the package build for some people (including me).

This patch does some general clean-up which also fixes the current issue.

• Uses consistent artifact naming
• Adds sbt support for this module
• Changes tests to use scalatest (fixes the original issue[1])

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.

[1] The original issue is that we need to allocate extra memory
for the tests, happens by default in our scalatest configuration.

[SparkQA]

Test build #22568 has started for PR 3025 at commit af2b785.

• This patch merges cleanly.

[aarondav]

LGTM!

[SparkQA]

Test build #22568 has finished for PR 3025 at commit af2b785.

• This patch fails MiMa tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/22568/
Test FAILed.

[pwendell]

@aarondav I didn't try MIMA with this new thing. I'll get it working and resubmit.

[pwendell]

Jenkins, test this please.

[SparkQA]

Test build #22586 has started for PR 3025 at commit faa9053.

• This patch merges cleanly.

[SparkQA]

Test build #22586 has finished for PR 3025 at commit faa9053.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/22586/
Test PASSed.

[aarondav]

Merging into master, thanks!