buildx/commands
Brian Goff 5e4444823c build: only use env for args if set
When following this pattern:

  buildx build --arg FOO

Where we want to pull `FOO` from env, currently we always set `FOO`
regardless if the `FOO` env var is even set.

This change makes it so that `FOO` would only be set if it has been set
in the env (even if it is set to empty).

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
..
imagetools imagetools: avoid printing newline on raw mode
bake.go new driver: kubernetes
build.go build: only use env for args if set
create.go driver: allow setting driver opts
inspect.go driver: allow configuring buildkitd flags
install.go install/uninstall: allow aliasing buildx to `docker builder`
ls.go vendor: update docker/cli (ab688a9a79a1) and docker/docker (3998dffb806f)
rm.go new driver: kubernetes
root.go rename to docker/buildx
stop.go commands: add implementations for create, use, rm, stop
uninstall.go install/uninstall: allow aliasing buildx to `docker builder`
use.go vendor: update docker/cli (ab688a9a79a1) and docker/docker (3998dffb806f)
util.go kubernetes: show Kubernetes Pods as buildx "Nodes" in `docker buildx inspect`
version.go rename to docker/buildx