Add setup to utilize buildkite for CI purposes:
1. .buildkite/hooks/pre-command:
* Handles getting git checkout setup against upstream repo
* Setup some west module cache (dirs, clean out files & locks)
* init dir for ccache
2. .buildkite/hooks/post-command:
* Report disk usage (meant for possible debugging)
3. .buildkite/pipeline.yml [uses to determine what to do]:
* setup zephyr env vars
* set which docker container to use
(export some local disk caches for git, west modules, and ccache)
* uses plug to general build annotation on failure (junit-annotate)
4. .buildkite/run.sh [ buildkite wrapper to invoke scripts/ci/run.sh ]
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
