set up travis (bug 1050156)

The test fix is to properly isolate it. In jenkins and locally, the tests running in their current order made it that the `tmp/packager` folder was created before this test ran.

The current [travis builds](https://travis-ci.org/magopian/olympia/builds) "only" have two failures (to be investigated, @davidbgk do you have a clue? FYI the https://travis-ci.org/magopian/olympia/builds/31926210 build has additional output), which is good enough as a starting point I believe ;)
well, that would still break locally if by bad luck you don't have the correct order of tests... which you just can't control... If it's only the "try" that annoys you, I can first check for existence. I'll do that ;)