OVN is used by default, which includes DVR and requires a Neutron
external network bridge on the Compute nodes. This change adds the
tag 'external_bridge' to the Controller roles and modifies the
overcloud-resource-registry-puppet.j2.yaml file to set the default
NIC configuration to net-config-bridge.yaml when this tag is set.
This will cause both Controller and Compute nodes to have an
external bridge by default if no specific NIC configuration files
are specified for both roles since the 'external_bridge' tag is set
This change also stops using net-config-bridge.yaml when the role
includes the 'controller' tag, since the 'external_bridge' tag is
used instead. A release note explains the change. This change is
being backported from the Victoria master branch.
(cherry picked from commit bc5b6133f1f192c7fe5330bc1fa13f8259eb9050)