Fix tests: allow to confige DB user and "set -e"

I consider "set -e" to be quite important here, otherwise you might install your current environment (e.g. if python-3.3 is not available etc).

I am new to PostgreSQL, and it might be specific to Debian/Ubuntu, but I have seen that there is a pg_virtualenv command, which takes care of setting up a cluster for tests: http://manpages.ubuntu.com/cgi-bin/search.py?q=pg_virtualenv