Add plugin code

This adds basic plugins.
"main" types: veth, bridge, macvlan
"ipam" type: host-local

The code has been ported over from github.com/coreos/rkt project
and adapted to fit the CNI spec.

scripts/docker-run.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# Run a docker container with network namespace set up by the
+# CNI plugins.
+
+# Example usage: ./docker-run.sh --rm busybox /sbin/ifconfig
+
+contid=$(docker run -d --net=none busybox:latest /bin/sleep 10000000)
+pid=$(docker inspect -f '{{ .State.Pid }}' $contid)
+netnspath=/proc/$pid/ns/net
+
+./exec-plugins.sh add $netnspath
+
+function cleanup() {
+	./exec-plugins.sh del $netnspath
+	docker kill $contid >/dev/null
+}
+trap cleanup EXIT
+
+docker run --net=container:$contid $@
+