Configure so that the vagrant user doesn't need to provide username and password.
apt-get -yqq install postgresql postgresql-contrib-9.3 libpq-dev postgresql-server-dev-9.3
su - postgres
createuser --createdb --superuser -Upostgres vagrant
psql -c "ALTER USER vagrant WITH PASSWORD 'password';"
psql -c "create database discourse_development owner vagrant encoding 'UTF8' TEMPLATE template0;"
psql -c "create database discourse_test owner vagrant encoding 'UTF8' TEMPLATE template0;"