[Fix] Improve idempotence of creating MAAS domains

- Need to refresh the local copy of existing domains
  during a deployment so that the same domain is not attempted
  to be created multiple times.

Change-Id: Idb792561690d2014aa2fceb54bf85c8e27cd91db

drydock_provisioner/drivers/node/maasdriver/actions/node.py

@@ -523,6 +523,7 @@ class CreateNetworkTemplate(BaseMaasAction):
                             name=n.dns_domain,
                             authoritative=False)
                         domain = domains.add(domain)
+                        domains.refresh()
 
                     subnet = subnets.singleton({'cidr': n.cidr})