firewall: new plugin which allows a host interface to send/receive traffic

Distros often have additional rules in the their iptabvles 'filter' table
that do things like:

-A FORWARD -j REJECT --reject-with icmp-host-prohibited

docker, for example, gets around this by adding explicit rules to the filter
table's FORWARD chain to allow traffic from the docker0 interface.  Do that
for a given host interface too, as a chained plugin.

plugins/meta/firewall/firewall_suite_test.go

@@ -0,0 +1,27 @@
+// Copyright 2017 CNI authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+
+	"testing"
+)
+
+func TestFirewall(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "firewall Suite")
+}