First step in the modernization of our RBE stack (see
go/rbe-tech-debt-notes).
- Get rid of the deprecated rbe_autoconfig and start using
[rbe_configs_gen](https://github.com/bazelbuild/bazel-toolchains#rbe_configs_gen---cli-tool-to-generate-configs)
+ check in the generated toolchain configs.
- Switch from marketplace.gcr.io/google/rbe-ubuntu16-04 to
marketplace.gcr.io/google/rbe-ubuntu18-04 (this image is still not owned
by us, but at least it's newer and demonstrates how a switch to a newer
docker image is done).
- provide script for generating the linux RBE toolchain configs.
- cleanup RBE configuration in the bazelrc files used for remote build
* refactor RBE configs
* better naming for linux specific RBE configs
* update names of RBE configs elsewhere
* move partial configs to tools/remote_build/include
Jan Tattermusch