Allow creating Stack for non centos images

This patch updates nodepool-setup and multinodes
roles to work with non centos images. It updates following:-

- Add a role variable: "default_image_user" which defaults to
  'centos'. It can be used to configure image_user like 'fedora'.
- Use 'package' module instead of 'yum' so it can work with non
  yum systems.
- yum_contentdir is not needed for Fedora, so skipped.
- centos-release-openstack and epel repos are not needed for
  Fedora, so skipped.

Change-Id: Ia1245a423e608273120b2c6b9668e2126073cccc

roles/multinodes/defaults/main.yml

@@ -31,3 +31,4 @@ subnode_flavor: m1.large
 subnode_groups:
   - subnodes
 nodepool_user: zuul
+default_image_user: centos

roles/multinodes/tasks/main.yml

@@ -128,7 +128,7 @@
     name: "subnode-{{ item.0 }}"
     hostname: "{{ item.1.1 }}"
     groups: "{{ subnode_groups| join(',') }}"
-    ansible_user: centos
+    ansible_user: "{{ default_image_user }}"
     ansible_host: "{{ item.1.1 }}"
     ansible_fqdn: "subnode-{{ item.0 }}"
     ansible_private_key_file: "{{ private_key_location }}"
@@ -139,7 +139,7 @@
 
 - name: Wait for provisioned hosts to become reachable
   command:
-    ssh -o BatchMode=yes -o "StrictHostKeyChecking=no" centos@{{ hostvars[item].ansible_host }} -i "{{ private_key_location }}"
+    ssh -o BatchMode=yes -o "StrictHostKeyChecking=no" {{ default_image_user }}@{{ hostvars[item].ansible_host }} -i "{{ private_key_location }}"
   register: result
   until: result is success
   retries: 100

roles/nodepool-setup/tasks/main.yml

@@ -30,7 +30,7 @@
     path: /etc/yum/vars/contentdir
   register: yum_contentdir
 
-- when: not yum_contentdir.stat.exists
+- when: not yum_contentdir.stat.exists and ansible_distribution|lower != 'fedora'
   block:
 
     - name: Discover package architecture
@@ -63,9 +63,10 @@
     - centos-release-openstack-ocata
     - epel-release
   become: true
+  when: ansible_distribution|lower != 'fedora'
 
 - name: Install packages
-  yum:
+  package:
     name: "{{ packages_list }}"
     state: latest
   become: true
@@ -140,7 +141,7 @@
   block:
 
     - name: Update packages
-      yum:
+      package:
         name: '*'
         state: latest
       become: true