Add support for sd_notify

Signed-off-by: Dan Walsh <dwalsh@redhat.com>

vendor/src/github.com/coreos/go-systemd/daemon/sdnotify.go

@@ -0,0 +1,31 @@
+// Code forked from Docker project
+package daemon
+
+import (
+	"errors"
+	"net"
+	"os"
+)
+
+var SdNotifyNoSocket = errors.New("No socket")
+
+// SdNotify sends a message to the init daemon. It is common to ignore the error.
+func SdNotify(state string) error {
+	socketAddr := &net.UnixAddr{
+		Name: os.Getenv("NOTIFY_SOCKET"),
+		Net:  "unixgram",
+	}
+
+	if socketAddr.Name == "" {
+		return SdNotifyNoSocket
+	}
+
+	conn, err := net.DialUnix(socketAddr.Net, nil, socketAddr)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	_, err = conn.Write([]byte(state))
+	return err
+}