Neutron-server should be on control group

It's convenient for tools/init-runonce work properly
Closes-Bug: #1503999
backport: liberty
Change-Id: I2d9f97e59ae4de3404f95a5231103cdd40a68835

ansible/inventory/multinode

@@ -104,7 +104,7 @@ nova
 
 # Neutron
 [neutron-server:children]
-neutron
+control
 
 [neutron-agents:children]
 neutron

ansible/roles/neutron/tasks/config.yml

@@ -141,7 +141,7 @@
   template:
     src: "roles/neutron/templates/neutron-agents.json.j2"
     dest: "{{ node_config_directory }}/neutron-agents/config.json"
-  when: inventory_hostname in groups['neutron-server']
+  when: inventory_hostname in groups['neutron-agents']
 
 - name: Copying Neutron Server JSON configuration file
   template: