Add `:scalastyle_integration` test to `:integration` test target
Review Request #2830 - Created Sept. 15, 2015 and submitted
This target seems to have been left out unintentionally so it's not currently being exercised by the integration tests.
I'm relying on travis to test this since the only way to exercise this code change is to run the
Travis link: https://travis-ci.org/pantsbuild/pants/builds/80542329