Update comments and add enable_haproxy to let helpinners know how
to set kolla_internal_vip_address and deploy AIO OpenStack without
haproxy correctly.
As a beginner in kolla-ansible, current comments for
kolla_internal_vip_address let me belive that if I set it to my eth0 ip,
kolla-ansible will help deploy an AIO OpenStack without haproxy. But in
fact it throws an error, I get the right way after searching IRC log.
Change-Id: I1ba1ffe774ad0cf29543523a56854b9d7caa680a
7d62a1c3ba