Vendor updated docker/distribution package

Fixes #19400

Note that this introduces an incompatibility with Docker 1.10-rc1,
because the media type used for schema1 manifests has been corrected in
the upstream distribution code. Docker 1.10-rc1 won't be able to pull
old manifests from Registry 2.3-rc0 and up, but because of this vendor
update, Docker 1.10-rc2 won't have this problem.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>