improve logging of dns entry creation
improve logging of dns entry creation

- log inside the lock, so we get proper serialisation
- include the container name, so we can identify the specific entry

weaveworks/weave,paulbellamy/weave,n054/weave,weaveworks/weave,n054/weave,dpw/weave,n054/weave,paulbellamy/weave,weaveworks/weave,weaveworks/weave,paulbellamy/weave,dpw/weave,n054/weave,n054/weave,dpw/weave,dpw/weave,paulbellamy/weave,dpw/weave