[SPARK-7224] [SPARK-7306] mock repository generator for --packages tests without nio.Path

The previous PR for SPARK-7224 (#5790) broke JDK 6, because it used java.nio.Path, which was in jdk 7, and not in 6. This PR uses Guava's `Files` to handle directory creation, and etc...

The description from the previous PR:
> 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 also rand the flaky test about 20 times locally, it didn't fail a single time, but I think it may fail like once every 100 builds? I still haven't figured the cause yet, but the test before it, `--jars` was also failing after we turned off the `--packages` test in `SparkSubmitSuite`. It may be related to the launch of SparkSubmit.

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #5892 from brkyvz/maven-utils and squashes the following commits:

e9b1903 [Burak Yavuz] fix merge conflict
68214e0 [Burak Yavuz] remove ignore for test(neglect spark dependencies)
e632381 [Burak Yavuz] fix ignore
9ef1408 [Burak Yavuz] re-enable --packages test
22eea62 [Burak Yavuz] Merge branch 'master' of github.com:apache/spark into maven-utils
05cd0de [Burak Yavuz] added mock repository generator