reenable this integration test. don't assume goal test retcode is 0 on success

I previously commented out this test, which was breaking in Travis-CI.

It assumed the exit code was 0 on success.
Empirical evidence suggests that's not always true for 'goal test'
in Travis-CI within a PantsRunIntegrationTest.
(Yeah, that's weird: https://github.com/pantsbuild/pants/issues/254)
So invoke './pants goal compile' instead; that still tests the scala-java stuff.

While I was in there, printed more info in the assert.

Testing Done:
on my laptop: ./pants goal test tests/python/pants_test/targets:integration
on Travis-CI: https://travis-ci.org/pantsbuild/pants/builds/27914227

Bugs closed: 250

Reviewed at https://rbcommons.com/s/twitter/r/569/