Default docker_puppet_debug to false

This isn't set unless the playbook is run via heat, so default it to false
to enable easier use via ansible-playbook combined with tripleo-ansible-inventory

Change-Id: I9705e4533831a019dd0051e5522d4b7958682506

common/deploy-steps-tasks.yaml

@@ -27,7 +27,7 @@
       shell: python /var/lib/docker-puppet/docker-puppet.py
       environment:
         NET_HOST: 'true'
-        DEBUG: '{{docker_puppet_debug}}'
+        DEBUG: '{{docker_puppet_debug|default(false)}}'
       when: step == "1"
       changed_when: false
       check_mode: no