Workaround for Bifrost being unable to write to /etc/hosts

Bifrost cannot modify /etc/hosts from within a container, so add a
host entry during bootstrap.

This was previously fixed by Ied378b4dd755788e75ad1814cecb5700732ba83e
but the logic in bifrost was changed [1], making it out of sync with
kolla-ansible, and triggering a write to /etc/hosts. This change applies
the new logic in bifrost to kolla-ansible, ensuring that the file will
not need to change in the container.

Longer term we should look at ways to make bifrost less eager to modify
/etc/hosts, accepting any file that will work for RabbitMQ.

[1]
60b9a9917e

Change-Id: I0ee05feae3630435b2ec52cfeddf33647a974ee0
Closes-Bug: #1661009

ansible/roles/bifrost/tasks/config.yml

@@ -35,15 +35,16 @@
     - { src: "id_rsa.pub", dest: "id_rsa.pub" }
     - { src: "ssh_config", dest: "ssh_config" }
 
-# NOTE(mgoddard): The following two tasks were lifted from the Bifrost plays.
-# Because Bifrost cannot modify /etc/hosts from within the container we must
-# do it here.
-- name: "RabbitMQ - Testing if hostname is defined in /etc/hosts"
-  command: grep -i "{{ ansible_hostname }}" /etc/hosts
-  ignore_errors: yes
-  register: test_grep_fix_hostname
-
-- name: "RabbitMQ - Fixing /etc/hosts"
-  command: sed -i 's/localhost/{{ ansible_hostname }} localhost/' /etc/hosts
-  when: test_grep_fix_hostname.rc != 0
-  become: True
+# NOTE(mgoddard): The following task was lifted from a Bifrost play
+# (playbooks/roles/bifrost-ironic-install/tasks/bootstrap.yml).  Because
+# Bifrost cannot modify /etc/hosts from within the container we must do it
+# here.
+- name: "Ensure /etc/hosts has good defaults"
+  lineinfile:
+    dest: "/etc/hosts"
+    regexp: "{{ item.regexp }}.*({{ ansible_hostname }}|localhost).*"
+    line: "{{ item.contents }}"
+  with_items:
+    - { regexp: '^127\.0\.0\.1', contents: '127.0.0.1 {{ ansible_hostname }} {{ ansible_fqdn }} localhost' }
+    - { regexp: '^::1', contents: '::1 {{ ansible_hostname }} {{ ansible_fqdn }} localhost ipv6-localhost ipv6-loopback' }
+  become: true