Incorrect plugin path

[stefanopiovesan]

A small issue: in the test_protoc.bat the plugin folder should be corrected:

set protoc_path_p=%path%\..\grpc\bin\grpc_protoc_plugins
and change:
%protoc_path%\protoc.exe helloworld.proto --grpc_out=%output_client_path% --plugin=protoc-gen-grpc=%protoc_path_p%\grpc_cpp_plugin.exe --proto_path=.\

%protoc_path%\protoc.exe helloworld.proto --grpc_out=%output_server_path% --plugin=protoc-gen-grpc=%protoc_path_p%\grpc_cpp_plugin.exe --proto_path=.\

[plasticbox]

@stefanopiovesan , @fredchyan
Thanks ;)