Bug 1094151 - Write a test to install & launch a packaged app from the M...

...arketplace
Per your comment and [Krupa's](https://bugzilla.mozilla.org/show_bug.cgi?id=1094151#c16), shouldn't we replace ```'%s,https://marketplace-dev.allizom.org' % default_trusted_locations``` by ```'*'```?