Instead of requiring the user to define an env.d override to deploy
etcd when Calico is used, we can provide a default etcd environment
definition that will only deploy etcd containers if 'etcd_hosts'
are defined in the openstack_user_config.
There is no upgrade impact because users who already use calico
will have an out of tree environment defintion in
/etc/openstack_deploy/env.d which overrides the in-tree version.
Change-Id: Id395ae972ea821b36f3b4ae09f4c72280256e676
05f36014c2