add DHCP IPAM plugin

The plugin binary actually functions in two modes. The first mode
is a regular CNI plugin. The second mode (when stared with "daemon" arg)
runs a DHCP client daemon. When executed as a CNI plugin, it issues
an RPC request to the daemon for actual processing. The daemon is
required since a DHCP lease needs to be maintained by periodically
renewing it. One instance of the daemon can server arbitrary number
of containers/leases.

scripts/priv-net-run.sh

@@ -2,7 +2,6 @@
 
 # Run a command in a private network namespace
 # set up by CNI plugins
-
 contid=$(printf '%x%x%x%x' $RANDOM $RANDOM $RANDOM $RANDOM)
 netnspath=/var/run/netns/$contid
 
@@ -17,4 +16,4 @@ function cleanup() {
 }
 trap cleanup EXIT
 
-ip netns exec $contid $@
+ip netns exec $contid "$@"