[SPARK-7224] added mock repository generator for --packages tests

This patch contains an `IvyTestUtils` file, which dynamically generates jars and pom files to test the `--packages` feature without having to rely on the internet, and Maven Central.

cc pwendell I know that there existed Util functions to create Jars and stuff already, but they didn't really serve my purposes as they appended random prefixes that was breaking things.

I also added the local repository tests. Notice that they work without passing the `repo` to `resolveMavenCoordinates`.

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #5790 from brkyvz/maven-utils and squashes the following commits:

3ec79b7 [Burak Yavuz] addressed comments v0.2
a39151b [Burak Yavuz] address comments v0.1
172dfef [Burak Yavuz] use Ivy format
7476d06 [Burak Yavuz] added mock repository generator