Include the runbook user into the docker group

Change-Id: Ib270d4ed0d5299d9d86254162e245d7c0037a31b
diff --git a/rundeck/client/runbook.yml b/rundeck/client/runbook.yml
index cb94025..27abaa6 100644
--- a/rundeck/client/runbook.yml
+++ b/rundeck/client/runbook.yml
@@ -9,6 +9,8 @@
           name: ${_param:rundeck_runbook_user}
           system: true
           sudo: true
+          groups:
+            - docker
           full_name: Rundeck Remote
           home: /var/lib/runbook
   openssh: