[SPARK-5289]: Backport publishing of repl, yarn into branch-1.2.

[pwendell]

This change was done in SPARK-4048 as part of a larger refactoring,
but we need to backport this publishing of yarn and repl into Spark
1.2, so that we can cut a 1.2.1 release with these artifacts.

[SparkQA]

Test build #25684 has started for PR 4079 at commit 807b833.

• This patch merges cleanly.

[vanzin]

Hi @pwendell , just want to make sure you're doing this for the right reasons. The change I made in SPARK-4048 wasn't so that these artifacts would be published, but because that enables running specific modules in the maven build directly (instead of running the whole build just to re-build a specific module).

[SparkQA]

Test build #25684 has finished for PR 4079 at commit 807b833.

• 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/25684/
Test PASSed.

[pwendell]

@vanzin I tried to cover it in #4080 - but basically there were changes you made that were anyways being requested by others in the community (asking us to publish these to Maven, which we did prior to 1.2).

[pwendell]

Okay I'm pulling these two in. I think we're all on the same page.