Add NodeCreateBatchSize parameter

This uses the heat resource group batched create feature to ensure
we don't create more than 30 nodes at a time, which has been reported
as the maximum supported by the default ironic ipxe/TFTP configuration.

Closes-Bug: #1688550
Change-Id: If3651e4c465d8d7bd4c8f2b48d45b1272ff2d272
Depends-On: I3551456664daf89d01f98bde85d7fb22a01d4a03
(cherry picked from commit 129881f2c6)

overcloud.j2.yaml

@@ -114,6 +114,11 @@ parameters:
     description: What interface to add to the HypervisorNeutronPhysicalBridge.
     type: string
 
+  NodeCreateBatchSize:
+    default: 30
+    description: Maxiumum batch size for creating nodes
+    type: number
+
   # Jinja loop for Role in role_data.yaml
 {% for role in roles %}
   # Parameters generated for {{role.name}} Role
@@ -344,6 +349,9 @@ resources:
   {{role.name}}:
     type: OS::Heat::ResourceGroup
     depends_on: Networks
+    update_policy:
+      batch_create:
+        max_batch_size: {get_param: NodeCreateBatchSize}
     properties:
       count: {get_param: {{role.name}}Count}
       removal_policies: {get_param: {{role.name}}RemovalPolicies}