Support deploying OVN as container services

Support deploying OVN as container services

This patch adds the support to containerize OVN services for the
base profile.

OVN db servers do not support active-active mode yet. It does support
master-slave mode supported through pacemaker, which will be supported
in a later patch.

Presently the tripleo container framework doesn't allow to start a
container in only controller 0 (or bootstrap node). OVN db servers and
ovn-northd are started on all the controllers, but only the OVN db
servers running in the boot strap controller are configured to listen
on the tcp ports 6641 and 6642. OVN neutron mechanism driver
and ovn-controller's use the ovn_dbs_vip to connect to the OVN db servers.
Haproxy configures all the controllers as back ends, but only OVN db
servers running on controller 0 respond since only they are configured
properly.

The OVN containers running on other controller nodes do not interact
any way, but are wasteful resources.

This patch also adds the scenario007-multinode-containers CI template.

Partial-bug: #1699085
Change-Id: I98b85191cc1fd8c2b166924044d704e79a4c4c8a
(cherry picked from commit e7cd03d2f0fcd8e3069246ced94f1a83869b8bea)