Fix kolla_docker_namespace comment

The default was updated in I5d49279fa9a2a263d84c6f468c00d4c8538c538c
but not the comment.

TrivialFix

Change-Id: I02909f2df9ab6f3c526785f2770fcd7a52063683
Signed-off-by: Doug Szumski <doug@stackhpc.com>

Author: dougszumski

etc/kayobe/kolla.yml

@@ -86,7 +86,7 @@
 # case Quay.io will be used.
 #kolla_docker_registry:
 
-# Docker namespace to use for Kolla images. Default is 'kolla'.
+# Docker namespace to use for Kolla images. Default is 'openstack.kolla'.
 #kolla_docker_namespace:
 
 # Username to use to access a docker registry. Default is not set, in which