packstack, fix get facts, get tempest_default_ip

Set facts was assuming a specific user in multiple
locations.  Use the tempest_default_ip variable in lieu
of ansible_default_ipv4.  I don't think its possible
to have a play on one host while using the hostvars
from another host. So now the ip's are set in set_facts
and used later by the tempest playbook

Change-Id: Iccbba97230b7adf17e8886f5a2319943afe328ba