This patch creates interfaces in builder/ for building Docker images.
It is a first step in a series of patches to remove the daemon
dependency on builder and later allow a client-side Dockerfile builder
as well as potential builder plugins.
It is needed because we cannot remove the /build API endpoint, so we
need to keep the server-side Dockerfile builder, but we also want to
reuse the same Dockerfile parser and evaluator for both server-side and
client-side.
builder/dockerfile/ and api/server/builder.go contain implementations
of those interfaces as a refactoring of the current code.
Signed-off-by: Tibor Vass <tibor@docker.com>
