Your right about that, downloading the archive, installing all the eggs, and then updating the database takes a bit of time (especially if you're like me and like re-running tests on nearly every change you make :P).  I think it would be cool to have a pre-package Galaxy for integration testing which is quick to setup.  I once thought of downloading Björn's Docker image from Galaxy Bootstrap and using it that way, but thinking is about as far as I got with that one.  One problem I could see is it would have to be re-built on every release of Galaxy you want to test against (whereas mercurial cloning/pulling makes sure you're always up to date with the latest code).