Header insert on gRPC code gen touched too many files

Header now only goes in generated files, as appropriate.

Also updated the header boilderplate to Copyright 2018
such that any new generation of code will be updated to the
new year.

Author: markmandel

build/boilerplate.go.txt

@@ -1,4 +1,4 @@
-// Copyright 2017 Google Inc. All Rights Reserved.
+// Copyright 2018 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.

build/build-image/gen-grpc-cpp.sh

@@ -18,7 +18,7 @@ cd /go/src/github.com/agonio/agon
 protoc -I . --grpc_out=./sdks/cpp --plugin=protoc-gen-grpc=`which grpc_cpp_plugin` sdk.proto
 protoc -I . --cpp_out=./sdks/cpp sdk.proto
 mkdir /tmp/cpp
-ls ./sdks/cpp | xargs -I@ bash -c "cat ./build/boilerplate.go.txt ./sdks/cpp/@ >> /tmp/cpp/@"
+find ./sdks/cpp/ -type f \( -name '*.pb.cc' -or -name '*.pb.h' \) -printf "%f\n" | xargs -I@ bash -c "cat ./build/boilerplate.go.txt ./sdks/cpp/@ >> /tmp/cpp/@"
 # already has a header, so we'll remove it
 rm /tmp/cpp/sdk.grpc.pb.h
 mv /tmp/cpp/* ./sdks/cpp/