Use cluster name for fixed_network instead of private

At present, when a fixed_network is not specified, it is given the name
"private" by default. When multiple clusters are created, we end up in a
situation where we end up with multiple networks all with the same name.
This PS intends to make it easier to see where the resources belong to
by using the cluster name.

Story: 2007460
Task: 39139

Change-Id: I7f8028b716f9a9eced17d85ca2e46e2b1e34875f

magnum/drivers/heat/k8s_template_def.py

@@ -185,6 +185,8 @@ class K8sTemplateDefinition(template_def.BaseTemplateDefinition):
         net_name = neutron.get_fixed_network_name(context, fixed_network)
         if net_name:
             extra_params['fixed_network_name'] = net_name
+        else:
+            extra_params['fixed_network_name'] = cluster.name
 
         # NOTE(brtknr): Convert fixed subnet name to UUID. If fixed_subnet
         # is not specified in cluster template use 'private' as the default

magnum/drivers/k8s_fedora_atomic_v1/templates/kubecluster.yaml

@@ -81,7 +81,6 @@ parameters:
   fixed_network_name:
     type: string
     description: name of a private network to use to provision machines
-    default: "private"
 
   fixed_subnet:
     type: string

magnum/drivers/k8s_fedora_coreos_v1/templates/kubecluster.yaml

@@ -81,7 +81,6 @@ parameters:
   fixed_network_name:
     type: string
     description: name of a private network to use to provision machines
-    default: "private"
 
   fixed_subnet:
     type: string