message: Add make clean to reduce sdk image size.
diff: @@ -17,6 +17,9 @@ export CC=gcc-7
  export CXX=g++-7
  export CPP=cpp-7
  +# get $HOME
  +cd
  +
  # specific version of protobufs to match the pre-compiled support libraries
  git clone https://github.com/protocolbuffers/protobuf
  cd protobuf
  