Limit hostfile generation to control nodes

With current implementation generation of hostfile is N^2, let's at
least limit this to controller nodes. Currently only RabbitMQ requires
hostnames, and these lands on control.

TrivialFix

Change-Id: I15f8d98386ede8bbc89f66923f21547efe20ff37

ansible/roles/baremetal/tasks/append_to_etc_hosts.yml

@@ -2,12 +2,12 @@
 - name: get real node hostname
   shell: echo $(hostname)
   register: real_node_hostname
-  delegate_to: "{{ baremetal_node }}"
+  delegate_to: "{{ control_node }}"
 
 - name: get real node ip
-  shell: ip -4 addr show "{{ hostvars[baremetal_node]['baremetal_nic'] }}" | grep -oP "(?<=inet )[\d\.]+(?=/)"
+  shell: ip -4 addr show "{{ hostvars[control_node]['baremetal_nic'] }}" | grep -oP "(?<=inet )[\d\.]+(?=/)"
   register: real_node_ip
-  delegate_to: "{{ baremetal_node }}"
+  delegate_to: "{{ control_node }}"
 
 - name: Insert hosts entries for all kolla-ansible hosts
   lineinfile:

ansible/roles/baremetal/tasks/pre-install.yml

@@ -39,9 +39,9 @@
   when: customize_etc_hosts | bool == True
 
 - include: append_to_etc_hosts.yml
-  with_inventory_hostnames: baremetal
+  with_inventory_hostnames: control
   loop_control:
-    loop_var: baremetal_node
+    loop_var: control_node
   become: True
   when: customize_etc_hosts | bool == True