Some of the network config templates shipped with tripleo-ansible
uses the `role_tags` in jinja2. For example:
roles/tripleo_network_config/templates/multiple_nics/multiple_nics.j2
elif network in role_networks or 'external_bridge' in role_tags
This change add's 'role_tags' to the network_config schema for
baremeteal deployment definition.
Closes-Bug: #2039008
Change-Id: I15e7e03c40d9334a665f7063df90bcddcccabfd4