Add network data for the undercloud

The undercloud needs the External network for the external VIP
address. It uses the _from_pool template creating a fake neutron
port.

Other networks are not required, and should be removed to optimize
the number of heat resources and plan rendering.

NOTE: Skips validation of network_data_undercloud.yaml against
network_data.yaml, as is already done to openshift and routed
networks networks data examples.

Related Bug: #1809313
Change-Id: Ib11a134df93e59947168b40bc71fb1da9172d4ac

network_data_undercloud.yaml

@@ -0,0 +1,3 @@
+- name: External
+  vip: true
+  name_lower: external

tools/yaml-validate.py

@@ -1125,8 +1125,9 @@ def validate(filename, param_map):
         # NOTE(mandre): Same goes for the openshift network data where it
         # contains only a subset of the overcloud networks.
         if (filename.startswith('./network_data_') and
-                not (filename.endswith('routed.yaml') or
-                     filename.endswith('openshift.yaml'))):
+                not filename.endswith(('routed.yaml',
+                                       'openshift.yaml',
+                                       'undercloud.yaml'))):
             result = validate_network_data_file(filename)
             retval |= result
         else: