support phpunit --log-junit option on 'oil test'

``oil test`` be support ``--log-junit`` option.

http://www.phpunit.de/manual/3.7/en/textui.html
`` --log-junit <file>        Log test execution in JUnit XML format to file.``

**Run example:**
``$ oil t --group=App --log-junit=build/testresult.xml``