Fix tests
Fix tests

This test has never worked correctly, it was only succeeding because we
logged "Creating XPI" in the wrong way (it was not stripped from the
output and showed up in the test stdout).

mozilla-jetpack/jpm,wagnerand/jpm,kkapsner/jpm,johannhof/jpm,kkapsner/jpm,wagnerand/jpm,mozilla/jpm,freaktechnik/jpm,johannhof/jpm,alexduch/jpm,kkapsner/jpm,johannhof/jpm,mozilla-jetpack/jpm,alexduch/jpm,mozilla-jetpack/jpm,wagnerand/jpm,mozilla/jpm,freaktechnik/jpm,alexduch/jpm,mozilla/jpm,freaktechnik/jpm