shorter hostname for cobald container

roles/cobald/tasks/main.yml

@@ -111,7 +111,7 @@
     image: cobald
     hostname: |-
       {{cobald_container_info.container.Config.Hostname | default('cobald-'+
-        lookup('password', '/dev/null chars=ascii_lowercase')) }}
+        lookup('password', '/dev/null chars=ascii_lowercase length=6')) }}
     domainname: cobald.local
     volumes:
     - "~{{unpriv_user}}/cobald:/etc/cobald"