(gh-477) enables root for non-root users on ec2 hypervisor

- root login is not possible on ubuntu-amis
- provision is not possible without root

This Patch enables root when the host['user'] differs from "root"
okey so the only thing we need to do then is to inform the user in a readme, that no standard ami from either ubuntu or amazon linux will work, and that a beaker user needs to create its own ami with enabled root before using beaker then?