Add goal for Monkey Runner 

This new goal (and tests) allow to run multiple test programs via [monkey runner](http://developer.android.com/tools/help/monkeyrunner_concepts.html).

It supports : 

* all command line arguments of monkey runner (including additional plugin for monkey runnner testing)
* running multiple tests (python tests)
* command line options for tests
* running tests on multiple devices
* injection of device serial number into the monkey runner script (with examples to handle it inside scripts)
* Junit XML report generation

There is one last test I couldn't make working, I can't understand why. If you have a few minutes, please explain me why it didn't work (the exact same test, or so, worked for testing lint...). The tested has been commented out to ease future work. If you don't have time, please simply remove it.