Update 'addUser' to 'createUser'

The 'addUser' shell helper is DEPRECATED. Use 'createUser' instead.
TrivialFix

Change-Id: Ib8c7a8971f46328a666cf63f1914fe50c7067064

ansible/roles/ceilometer/tasks/bootstrap.yml

 ---
 - name: Creating Ceilometer MongoDB database
-  command: docker exec -t mongodb mongo --host {{ ceilometer_database_mongodb_address }} --eval 'db = db.getSiblingDB("{{ ceilometer_database_name }}"); db.addUser({user':' "{{ ceilometer_database_user }}", pwd':' "{{ ceilometer_database_password}}", roles':' [ "readWrite", "dbAdmin" ]})'
+  command: docker exec -t mongodb mongo --host {{ ceilometer_database_mongodb_address }} --eval 'db = db.getSiblingDB("{{ ceilometer_database_name }}"); db.createUser({user':' "{{ ceilometer_database_user }}", pwd':' "{{ ceilometer_database_password}}", roles':' [ "readWrite", "dbAdmin" ]})'
   register: mongodb_ceilometer_database
   run_once: true
   failed_when: