Generalize artifact builder

Compile Node library on Windows

Add {GPR,GRPC,CENSUS}_API tags to public functions

Remove host option from ServerConfig proto

Add comments to grpc_transport_stream_op structure

Release 0.12 -> master

Remove dead src/python/README.md.

Mitigate Python build directory naming conflict

may cause inter-language confusion.

Measure CPU costs on Jenkins Linux

Preparatory changes for work shedding

Don't bother with full build in java docker

On Mac and Windows, the default directory name conflicts with the BUILD
file we have.

Support mixing sync and async method in the same service + Separation of core from proto compiler output

Use correct path for C tests on Win 64

Testing scenarios for various performance characteristics

- cleanup: change grpc_iomgr_cb_func to take a bool instead of int
  success
- cleanup: follow through with iomgr callback scheduling functions
- prepare: add a workqueue to offload to to grpc_exec_ctx_enqueue*
  functions

The command in the docker image is just to prepare a cache to reduce
download for later builds. We only run installDist in build_interop.sh,
so don't bother with full build.

Fixes grpc/grpc-java#1370

Generate report.xml report with --build_only too

Toggle --build_only flag for portability tests via scenario name