Add networks to Standalone role

The standalone role can be used with and without an undercloud. If you
deploy it with an undercloud and use network-isolation, then the
deployment will fail because the networks aren't defined in the role.
Since it doesn't hurt to have them on in the non-undercloud version,
lets add them back in.  They were previously removed as part of
https://review.opendev.org/#/c/628265/

Change-Id: I366631cb6ecd39595c00204a02408beb431af70e
Closes-Bug: #1832043
(cherry picked from commit da1827f7d3)

roles/Standalone.yaml

@@ -12,6 +12,17 @@
     - primary
     - controller
     - standalone
+  networks:
+    External:
+      subnet: external_subnet
+    InternalApi:
+      subnet: internal_api_subnet
+    Storage:
+      subnet: storage_subnet
+    StorageMgmt:
+      subnet: storage_mgmt_subnet
+    Tenant:
+      subnet: tenant_subnet
   disable_constraints: True
   ServicesDefault:
     - OS::TripleO::Services::Aide