xserver-nodm-init: add EnvironmentFile

* used to set HOME variable before /etc/X11/Xsession is started
* e.g. enlightenment is creating ${HOME}/.e and without this it ends in
  /tmp/.e and during startup HOME gets defined and switched to
  /home/root/.e

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>