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 ;)
oh, really? I thought it was the opposite, that the "compress_assets" needed the statics collected already :/ I could try reverting this change, and see what happens ;)