Make neutron dhcp agents per network conditional

While the heat templates specify a default value of 3, it rarely seems
to have an effect as the tripleoclient is setting this according to the
controller scale. This was fine before composable roles, but it is now
invalid. While the client needs to be modified to no longer set this
according to controller scale, the template should default to a sentinel
value that will allow the puppet code to determine the proper value by
the number of hosts that have the neutron dhcp agent deployed on them.

Depends-On: I5533e42c5ba9f72cc70d80489a07e30ee2341198
Partial-bug: #1632721
Change-Id: I06628764c4769d91bbc42efe1c722702d6574d02

puppet/services/neutron-base.yaml

@@ -24,7 +24,7 @@ parameters:
     type: number
   NeutronDhcpAgentsPerNetwork:
     type: number
-    default: 3
+    default: 0
     description: The number of neutron dhcp agents to schedule per network
   NeutronCorePlugin:
     default: 'ml2'
@@ -72,17 +72,20 @@ parameters:
                  via parameter_defaults in the resource registry.
     type: json
 
+conditions:
+  dhcp_agents_zero: {equals : [{get_param: NeutronDhcpAgentsPerNetwork}, 0]}
+
 outputs:
   role_data:
     description: Role data for the Neutron base service.
     value:
       service_name: neutron_base
       config_settings:
-        neutron::rabbit_password: {get_param: RabbitPassword}
+        map_merge:
+          - neutron::rabbit_password: {get_param: RabbitPassword}
             neutron::rabbit_user: {get_param: RabbitUserName}
             neutron::rabbit_use_ssl: {get_param: RabbitClientUseSSL}
             neutron::rabbit_port: {get_param: RabbitClientPort}
-        neutron::dhcp_agents_per_network: {get_param: NeutronDhcpAgentsPerNetwork}
             neutron::core_plugin: {get_param: NeutronCorePlugin}
             neutron::service_plugins: {get_param: NeutronServicePlugins}
             neutron::debug: {get_param: Debug}
@@ -93,3 +96,7 @@ outputs:
             neutron::db::database_db_max_retries: -1
             neutron::db::database_max_retries: -1
             neutron::global_physnet_mtu: {get_param: NeutronGlobalPhysnetMtu}
+          - if:
+            - dhcp_agents_zero
+            - {}
+            - tripleo::profile::base::neutron::dhcp_agents_per_network: {get_param: NeutronDhcpAgentsPerNetwork}

releasenotes/notes/allow-neutron-dhcp-agents-per-network-calculation-536c70391497256d.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    NeutronDhcpAgents had a default value of 3 that, even though unused in
+    practice was a bad default value. Changing the default value to a
+    sentinel value and making the hiera conditional allows deploy-time
+    logic in puppet to provide a default value based on the number of dhcp
+    agents being deployed.