- [X] put multiples workers in a single binary ("-tags containerd standalone")
- [X] add worker selector to LLB vertex metadata
- [X] s/worker/executor/g
- [X] introduce the new "worker" concept https://github.com/moby/buildkit/pull/176#discussion_r153693928
- [X] fix up CLI
- [X] fix up tests
- allow using multiples workers (requires inter-vertex cache copier, HUGE!) --> will be separate PR
Implementation notes:
- "Workers" are renamed to "executors" now
- The new "worker" instance holds an "executor" instance and its
related stuffs such as the snapshotter
- The default worker is "runc-overlay"
Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>