Split resolver to only return a name with separate methods
for getting a fetcher and pusher. Add implementation for
push.
Signed-off-by: Derek McGowan <derek@mcgstyle.net>
Allow usage of the experimental docker resolver as a package. There are
very few changes to the consuming code, demonstrating the effectiveness
of the abstraction. This move will allow future contributions to a more
featured resolver implementation.
Signed-off-by: Stephen J Day <stephen.day@docker.com>