Use Env Variable rather than local_settings for allowed hosts

[pjdufour]

Ansible playbook alters ALLOWED_HOSTS in settings.py then fails on git sync because settings.py was changed. Better to use environmental variables with our current strategy.

ansible-geonode/tasks/geonode.yml

Line 81 in ab17551

- name: patch the settings.py file in place

==

TASK [GeoNode.geonode : checkout latest web app code] **************************
fatal: [default]: FAILED! => {"changed": false, "failed": true, "msg": "Local modifications exist in repository (force=no)."}