Fix dependency for nested attributes

Nested get_attr functions in {{network.name}}VirtualIP/VipMap
can't determine which attributes of Networks are used until
after ServiceNetMap's attribute values are available.

Change-Id: I418a06a59ff46feedcc22cb6f87b707fae3a9874

overcloud.j2.yaml

@@ -936,6 +936,10 @@ resources:
   # creates the network architecture
   Networks:
     type: OS::TripleO::Network
+    # Because of nested get_attr functions in *VirtualIP/VipMap,
+    # we can't determine which attributes of Networks are used until after
+    # ServiceNetMap's attribute values are available.
+    depends_on: ServiceNetMap
     properties:
       CtlplaneNetworkCidrs: {get_attr: [ControlVirtualIP, network, tags]}