This commit changes the automation scripts so that the base image
is built together with the rest of the supervisor. We use a hash of
the contents of the base-image folder as tag for the base image so
that unnecessary rebuilds are avoided.
The build scripts are also modified to always clean up the resulting base image
and the image used to build it. We use docker pull and push to enable caching.
Change-Type: patch
Signed-off-by: Pablo Carranza Velez <pablo@resin.io>
