Stop hardcoding host's config volume path
Stop hardcoding host's config volume path

Get the path from the CONFIG_VOLUME_PREFIX environment variable.

This is useful for debugging and generate configuration files to
a different directory.

Change-Id: Ib85e3898804312ebb6677a5fa189fbfc357ce27c

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates