Walrus BMI grpc server docker

[sverhoeven]

Similar to grpc4bmi it requires model maker to implement class (in this case walrus/walrus-bmi.r:WalrusBmi) of walrus/abstract-bmi.r:AbstractBmi class.

TODO:

• do not run whole model in initialize method, but perform steps in update* methods
• error handling, now server dies if error happens
• trying to use server reflection will kill server
• dont use fork https://github.com/eWaterCycle/grpc-r
• packaging,:

Would like to make Dockerfile like

FROM walrus
RUN  install.r grpc4bmi
ENV BMI_MODULE=WALRUS
ENV BMI_CLASS=WalrusBmi
ENV BMI_PORT=55555

CMD ["/usr/bin/bmi-server.r"]

but for now we are using more complicated dockerfile.