Abstract out diff implementations for importing

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

libcontainer/nsinit/state.go

@@ -0,0 +1,24 @@
+package nsinit
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+)
+
+type StateWriter interface {
+	WritePid(pid int) error
+	DeletePid() error
+}
+
+type DefaultStateWriter struct {
+}
+
+// writePidFile writes the namespaced processes pid to .nspid in the rootfs for the container
+func (*DefaultStateWriter) WritePid(pid int) error {
+	return ioutil.WriteFile(".nspid", []byte(fmt.Sprint(pid)), 0655)
+}
+
+func (*DefaultStateWriter) DeletePid() error {
+	return os.Remove(".nspid")
+}