chore(controller): update docker-py to 1.6.0

See https://github.com/docker/docker-py/blob/master/docs/change_log.md#160

Author: mboersma

rootfs/requirements.txt

@@ -8,7 +8,7 @@ django-guardian==1.2.5
 django-json-field==0.5.7
 django-auth-ldap==1.2.5
 djangorestframework==3.0.5
-docker-py==1.5.0
+docker-py==1.6.0
 gunicorn==19.3.0
 psycopg2==2.6.1
 python-etcd==0.3.2