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/tls/connect_tls.go

@@ -0,0 +1,51 @@
+package tls
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+
+	"github.com/pkg/errors"
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/tlsconf"
+	"github.com/zrepl/zrepl/transport"
+)
+
+type TLSConnecter struct {
+	Address   string
+	dialer    net.Dialer
+	tlsConfig *tls.Config
+}
+
+func TLSConnecterFromConfig(in *config.TLSConnect) (*TLSConnecter, error) {
+	dialer := net.Dialer{
+		Timeout: in.DialTimeout,
+	}
+
+	ca, err := tlsconf.ParseCAFile(in.Ca)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot parse ca file")
+	}
+
+	cert, err := tls.LoadX509KeyPair(in.Cert, in.Key)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot parse cert/key pair")
+	}
+
+	tlsConfig, err := tlsconf.ClientAuthClient(in.ServerCN, ca, cert)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot build tls config")
+	}
+
+	return &TLSConnecter{in.Address, dialer, tlsConfig}, nil
+}
+
+func (c *TLSConnecter) Connect(dialCtx context.Context) (transport.Wire, error) {
+	conn, err := c.dialer.DialContext(dialCtx, "tcp", c.Address)
+	if err != nil {
+		return nil, err
+	}
+	tcpConn := conn.(*net.TCPConn)
+	tlsConn := tls.Client(conn, c.tlsConfig)
+	return newWireAdaptor(tlsConn, tcpConn), nil
+}