Using docker build is slower and needs lots of Dockerfiles,
while a single image with a careful script can accept any type
of image, either with `-v` to share into `/tmp` for interactive
use (where you need the input and a tty, or by adding a tarball
for cases where there is no login such as running tests, so you
can still use a remote daemon in these cases.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
