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)

transport/ssh/connect_ssh.go

@@ -0,0 +1,55 @@
+package ssh
+
+import (
+	"context"
+	"github.com/jinzhu/copier"
+	"github.com/pkg/errors"
+	"github.com/problame/go-netssh"
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/transport"
+	"time"
+)
+
+type SSHStdinserverConnecter struct {
+	Host                 string
+	User                 string
+	Port                 uint16
+	IdentityFile         string
+	TransportOpenCommand []string
+	SSHCommand           string
+	Options              []string
+	dialTimeout          time.Duration
+}
+
+func SSHStdinserverConnecterFromConfig(in *config.SSHStdinserverConnect) (c *SSHStdinserverConnecter, err error) {
+
+	c = &SSHStdinserverConnecter{
+		Host:         in.Host,
+		User:         in.User,
+		Port:         in.Port,
+		IdentityFile: in.IdentityFile,
+		SSHCommand:   in.SSHCommand,
+		Options:      in.Options,
+		dialTimeout:  in.DialTimeout,
+	}
+	return
+
+}
+
+func (c *SSHStdinserverConnecter) Connect(dialCtx context.Context) (transport.Wire, error) {
+
+	var endpoint netssh.Endpoint
+	if err := copier.Copy(&endpoint, c); err != nil {
+		return nil, errors.WithStack(err)
+	}
+	dialCtx, dialCancel := context.WithTimeout(dialCtx, c.dialTimeout) // context.TODO tied to error handling below
+	defer dialCancel()
+	nconn, err := netssh.Dial(dialCtx, endpoint)
+	if err != nil {
+		if err == context.DeadlineExceeded {
+			err = errors.Errorf("dial_timeout of %s exceeded", c.dialTimeout)
+		}
+		return nil, err
+	}
+	return nconn, nil
+}