tests/docker: add --registry support to tooling

This allows us to point the tools towards a registry from which they
can grab pre-built layers instead of doing everything from scratch
each time. To enable this we need to be using the DOCKER_BUILDKIT
engine.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200701135652.1366-25-alex.bennee@linaro.org>
2 files changed