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)

daemon/prometheus.go

@@ -7,6 +7,7 @@ import (
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/daemon/job"
 	"github.com/zrepl/zrepl/logger"
+	"github.com/zrepl/zrepl/rpc/dataconn/frameconn"
 	"github.com/zrepl/zrepl/zfs"
 	"net"
 	"net/http"
@@ -49,6 +50,10 @@ func (j *prometheusJob) Run(ctx context.Context) {
 		panic(err)
 	}
 
+	if err := frameconn.PrometheusRegister(prometheus.DefaultRegisterer); err != nil {
+		panic(err)
+	}
+
 	log := job.GetLogger(ctx)
 
 	l, err := net.Listen("tcp", j.listen)