Remove UndercloudCtlplaneSubnets defaults in UC env

The defaults in environments/undercloud.yaml will be
merged with what the was defined in undercloud.conf.
If the 'ctlplane-subnet' is not used in undercloud.conf
the default is merged, and we end up with an additional
subnet that was not requested by the undercloud installed.

This change set the default to {} in:
  environments/undercloud.yaml

Also add's a comment to hightlight that there should be
a empty dict default.

Closes-Bug: #1820330
Change-Id: Idc17154b2e1e143ba4e84b9b96f5355fc9230172

environments/undercloud.yaml

@@ -119,8 +119,8 @@ parameter_defaults:
   IronicForcePowerStateDuringSync: false
   IronicInspectorCollectors: default,extra-hardware,numa-topology,logs
   IronicInspectorInterface: br-ctlplane
-  IronicInspectorSubnets:
+  # IronicInspectorSubnets:
-    - ip_range: '192.168.24.100,192.168.24.200'
+  #   - ip_range: '192.168.24.100,192.168.24.200'
   IronicProvisioningNetwork: 'ctlplane'
   IronicRescuingNetwork: 'ctlplane'
   ZaqarMessageStore: 'swift'
@@ -155,12 +155,20 @@ parameter_defaults:
   #     - ip_netmask: 192.168.26.0/24
   #       next_hop: 192.168.24.1
   ControlPlaneStaticRoutes: []
-  UndercloudCtlplaneSubnets:
+  # A dictionary of Undercloud ctlplane subnets.
-    ctlplane-subnet:
+  # NOTE(hjensas): This should be {} in this environment file, otherwise it may
-      NetworkCidr: '192.168.24.0/24'
+  # results in values set here being merged with the values set in
-      NetworkGateway: '192.168.24.1'
+  # undercloud.conf. See Bug: https://bugs.launchpad.net/tripleo/+bug/1820330
-      DhcpRangeStart: '192.168.24.5'
+  # Example:
-      DhcpRangeEnd: '192.168.24.24'
+  #   UndercloudCtlplaneSubnets:
+  #     ctlplane-subnet:
+  #       NetworkCidr: '192.168.24.0/24'
+  #       NetworkGateway: '192.168.24.1'
+  #       DhcpRangeStart: '192.168.24.5'
+  #       DhcpRangeEnd: '192.168.24.24'
+  #       HostRoutes:
+  #         - {'destination': '10.10.10.0/24', 'nexthop': '192.168.24.254'}
+  UndercloudCtlplaneSubnets: {}
   UndercloudCtlplaneLocalSubnet: 'ctlplane-subnet'
   MistralDockerGroup: true
   PasswordAuthentication: 'yes'

releasenotes/notes/fix-uc-ctlplane-subnet-defaults-merged-5a6061b29618f5cf.yaml

@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    Fixes an issue that caused a subnet to be wrongly created on the Undercloud
+    provisioning network based on environment default values. If the default
+    ``ctlplane-subnet`` was renamed in ``undercloud.conf``, the defaults for
+    ``ctlplane-subnet`` in ``environments/undercloud.yaml`` was merged with the
+    subnets defined in ``undercloud.conf``. See `bug 1820330
+    <https://bugs.launchpad.net/tripleo/+bug/1820330>`_.