docker: Integrate docker containers with Open vSwitch.

Open vSwitch does not have native integration with Docker.
INSTALL.Docker explains how Open vSwitch can be integrated
with docker non-natively.

ovs-docker is a helper script to add network interfaces to
docker containers and to attach them as ports to OVS bridge.
This script can be further enhanced as we understand different
use cases.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>