Make lb-mgmt-subnet a class B subnet

TripleO creates that subnet during the Octavia deployment process.
Currently, it is created as a class C subnet with allocation_pools
that essentially limit the number of address in that subnet to 150.

This patch enhances the lb-mgmt-subnet to be class B so the global
amount of Octavia loadbalancers won't be constrained to a very low
number.

Related-Bug: #1770956

Change-Id: I3465dd9e2f95983a3f3a5dcd85f50781044fd6ec

docker/services/octavia/octavia-deployment-config.yaml

@@ -83,21 +83,21 @@ parameters:
   OctaviaControlSubnetCidr:
     description: Subnet for amphora control subnet in CIDR form.
     type: string
-    default: '192.168.199.0/24'
+    default: '172.24.0.0/16'
   OctaviaControlSubnetGateway:
     description: IP address for control network gateway
     type: string
-    default: '192.168.199.1'
+    default: '172.24.0.1'
   OctaviaControlSubnetPoolStart:
     description: First address in amphora control subnet address
                  pool.
     type: string
-    default: '192.168.199.50'
+    default: '172.24.0.2'
   OctaviaControlSubnetPoolEnd:
     description: First address in amphora control subnet address
                  pool.
     type: string
-    default: '192.168.199.200'
+    default: '172.24.255.254'
   OctaviaCaCertFile:
     type: string
     default: '/etc/octavia/certs/ca_01.pem'

releasenotes/notes/update-lb-mgmt-subnet-to-class-b-1cd832ef08a30c85.yaml

@@ -0,0 +1,11 @@
+---
+features:
+  -
+    Enhance lb-mgmt-subnet to be a class B subnet, so the global amount
+    of Octavia loadbalancers won't be constrained to a very low number.
+upgrade:
+  -
+    This fix is changing the default mask for lb-mgmt-subnet.
+    Operators can either manually modify the already existing subnet or create
+    a new one and update Octavia to use it. Newly create loadbalancer will use
+    The newly created subnet.