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/grpcclientidentity/example/grpcauth.proto

@@ -0,0 +1,16 @@
+syntax = "proto3";
+
+package pdu;
+
+
+service Greeter {
+    rpc Greet(GreetRequest) returns (GreetResponse) {}
+}
+
+message GreetRequest {
+    string name = 1;
+}
+
+message GreetResponse {
+    string msg = 1;
+}