Make Ansible env variables configurable
Make Ansible env variables configurable

Some env variables set for the ansible-playbook execution were
hardcoded; this change configures them as a default workflow
input so they can be overridden from the called (tripleo templates).

Also adds to the list /var/log/mistral as default location
for the ceph-install workflow logging.

Change-Id: Ibf748c5ee579e4c84785b6ef7674ee32fc3573e5

openstack/tripleo-common,openstack/tripleo-common