WithNetNS restores original namespace when callback errors

- adds test coverage of WithNetNS in BDD-style

ns/ns_suite_test.go

@@ -0,0 +1,20 @@
+package ns_test
+
+import (
+	"math/rand"
+	"runtime"
+
+	. "github.com/onsi/ginkgo"
+	"github.com/onsi/ginkgo/config"
+	. "github.com/onsi/gomega"
+
+	"testing"
+)
+
+func TestNs(t *testing.T) {
+	rand.Seed(config.GinkgoConfig.RandomSeed)
+	runtime.LockOSThread()
+
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "pkg/ns Suite")
+}