Extend example playbook to contain valid values

In case of standalone deployment of the role, it's important to avoid
client-installation on server-side, as this causes a race condition,
where deployed my.cnf is used before the respective user is created.

Patch also adds all requirements which needed for the role execution
in a standalone mode.

Change-Id: I0900e1d413a80020ca4dfe7477499da25eb64689

examples/playbook.yml

@@ -2,9 +2,23 @@
 - name: Install Galera server
   hosts: galera_all
   user: root
+  serial:
+    - 1
+    - 100%
   roles:
     - galera_server
   vars:
     galera_install_server: true
+    # NOTE: it is important to disable client installation on
+    #       server, unless `galera_root_user: root` (default: admin)
+    galera_install_client: false
+    galera_root_password: secrete
+
+- name: Install Galera client
+  hosts: localhost
+  roles:
+    - galera_server
+  vars:
+    galera_install_server: false
     galera_install_client: true
     galera_root_password: secrete

requirements.yml

@@ -0,0 +1,21 @@
+---
+collections:
+- name: openstack.config_template
+  source: https://opendev.org/openstack/ansible-config_template
+  type: git
+  version: 2.1.1
+- name: community.general
+  source: https://github.com/ansible-collections/community.general
+  type: git
+  version: 10.0.1
+- name: community.mysql
+  source: https://github.com/ansible-collections/community.mysql
+  type: git
+  version: 3.11.0
+roles:
+- name: apt_package_pinning
+  src: git+https://opendev.org/openstack/openstack-ansible-apt_package_pinning
+  version: master
+- name: systemd_service
+  src: git+https://opendev.org/openstack/ansible-role-systemd_service
+  version: master