Introduce site_facts module

Because of a recent change to Ansible (in 1.6.7) the template var hack
that we were using no longer works. The site_facts module will now set
those facts. The tempest iptables role was also reworked to not need the
tempest_*_ip facts to be set.

Conflicts:
	roles/get_nodes/add_hosts/tasks/main.yml
	roles/set_facts/tasks/addl_vars.j2
	roles/set_facts/tasks/main.yml
	roles/tempest/iptables/defaults/main.yml
	roles/tempest/iptables/node_data/tasks/main.yml
	roles/tempest/iptables/tasks/main.yml

Change-Id: I36ea7e56b1081e308f7fd81353e504a81f272f90