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_shutdown_fsm.go

@@ -0,0 +1,37 @@
+package frameconn
+
+import "sync"
+
+type shutdownFSM struct {
+	mtx            sync.Mutex
+	state          shutdownFSMState
+}
+
+type shutdownFSMState uint32
+
+const (
+	shutdownStateOpen shutdownFSMState = iota
+	shutdownStateBegin
+)
+
+func newShutdownFSM() *shutdownFSM {
+	fsm := &shutdownFSM{
+		state:          shutdownStateOpen,
+	}
+	return fsm
+}
+
+func (f *shutdownFSM) Begin() (thisCallStartedShutdown bool) {
+	f.mtx.Lock()
+	defer f.mtx.Unlock()
+	thisCallStartedShutdown = f.state != shutdownStateOpen
+	f.state = shutdownStateBegin
+	return thisCallStartedShutdown
+}
+
+func (f *shutdownFSM) IsShuttingDown() bool {
+	f.mtx.Lock()
+	defer f.mtx.Unlock()
+	return f.state != shutdownStateOpen
+}
+