Make node join event logging less noisy
Make node join event logging less noisy

Commit 90103909401ecbe2b39216bb44dc79b89eee2b7e
added a number of debugging messages for node join/leave
events.

This patch checks if a node already was listed,
and otherwise skips the logging to make the logs a bit
less noisy.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

docker/libnetwork,abhi/libnetwork,ityangchen/libnetwork,abhi/libnetwork,vdemeester/libnetwork,docker/libnetwork,medallia/libnetwork,fcrisciani/libnetwork,allencloud/libnetwork,mahak/libnetwork,medallia/libnetwork,ityangchen/libnetwork,mahak/libnetwork,vdemeester/libnetwork,vdemeester/libnetwork,kolyshkin/libnetwork,kolyshkin/libnetwork,abhi/libnetwork,fcrisciani/libnetwork,allencloud/libnetwork,medallia/libnetwork,kolyshkin/libnetwork,mahak/libnetwork,docker/libnetwork