rpc rewrite: control RPCs using gRPC + separate RPC for data transfer

transport/ssh: update go-netssh to new version
    => supports CloseWrite and Deadlines
    => build: require Go 1.11 (netssh requires it)

rpc/dataconn/frameconn/frameconn_prometheus.go

@@ -0,0 +1,63 @@
+package frameconn
+
+import "github.com/prometheus/client_golang/prometheus"
+
+var prom struct {
+	ShutdownDrainBytesRead prometheus.Summary
+	ShutdownSeconds        prometheus.Summary
+	ShutdownDrainSeconds   prometheus.Summary
+	ShutdownHardCloses     *prometheus.CounterVec
+	ShutdownCloseErrors    *prometheus.CounterVec
+}
+
+func init() {
+	prom.ShutdownDrainBytesRead = prometheus.NewSummary(prometheus.SummaryOpts{
+		Namespace: "zrepl",
+		Subsystem: "frameconn",
+		Name:      "shutdown_drain_bytes_read",
+		Help:      "Number of bytes read during the drain phase of connection shutdown",
+	})
+	prom.ShutdownSeconds = prometheus.NewSummary(prometheus.SummaryOpts{
+		Namespace: "zrepl",
+		Subsystem: "frameconn",
+		Name:      "shutdown_seconds",
+		Help:      "Seconds it took for connection shutdown to complete",
+	})
+	prom.ShutdownDrainSeconds = prometheus.NewSummary(prometheus.SummaryOpts{
+		Namespace: "zrepl",
+		Subsystem: "frameconn",
+		Name:      "shutdown_drain_seconds",
+		Help:      "Seconds it took from read-side-drain until shutdown completion",
+	})
+	prom.ShutdownHardCloses = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: "zrepl",
+		Subsystem: "frameconn",
+		Name:      "shutdown_hard_closes",
+		Help:      "Number of hard connection closes during shutdown (abortive close)",
+	}, []string{"step"})
+	prom.ShutdownCloseErrors = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: "zrepl",
+		Subsystem: "frameconn",
+		Name:      "shutdown_close_errors",
+		Help:      "Number of errors closing the underlying network connection. Should alert on this",
+	}, []string{"step"})
+}
+
+func PrometheusRegister(registry prometheus.Registerer) error {
+	if err := registry.Register(prom.ShutdownDrainBytesRead); err != nil {
+		return err
+	}
+	if err := registry.Register(prom.ShutdownSeconds); err != nil {
+		return err
+	}
+	if err := registry.Register(prom.ShutdownDrainSeconds); err != nil {
+		return err
+	}
+	if err := registry.Register(prom.ShutdownHardCloses); err != nil {
+		return err
+	}
+	if err := registry.Register(prom.ShutdownCloseErrors); err != nil {
+		return err
+	}
+	return nil
+}