Add support for outputting test results in junit xml format

Conflicts:
	src/com/facebook/buck/java/JUnitStep.java
	src/com/facebook/buck/junit/JUnitRunner.java

Conflicts:
	src/com/facebook/buck/java/JUnitStep.java
	src/com/facebook/buck/junit/JUnitRunner.java
Merge branch 'feature/junit-compatible-test-output-2' into lmax-16

Conflicts:
	src/com/facebook/buck/java/JUnitStep.java
	src/com/facebook/buck/junit/JUnitRunner.java