Change dhcp plugin to send ClientID allowing container to have multiple CNI

interfaces using dhcp ipam.

Vendor latest dhcp4server, dhcp4client, dhcp4

Added additional tests for new functionality in dhcp2_test.go

Wrap d2g dhcp4client calls with our own which add clientID to packet.

vendor/github.com/d2g/dhcp4/packet.go

@@ -127,10 +127,11 @@ func ReplyPacket(req Packet, mt MessageType, serverId, yIAddr net.IP, leaseDurat
 	p.SetYIAddr(yIAddr)
 	p.SetGIAddr(req.GIAddr())
 	p.SetCHAddr(req.CHAddr())
-	p.SetSecs(req.Secs())
 	p.AddOption(OptionDHCPMessageType, []byte{byte(mt)})
 	p.AddOption(OptionServerIdentifier, []byte(serverId))
-	p.AddOption(OptionIPAddressLeaseTime, OptionsLeaseTime(leaseDuration))
+	if leaseDuration > 0 {
+		p.AddOption(OptionIPAddressLeaseTime, OptionsLeaseTime(leaseDuration))
+	}
 	for _, o := range options {
 		p.AddOption(o.Code, o.Value)
 	}