Generate md5 and sha265 hashes when building, and upload them in hack/release.sh

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
whitespace-blind

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #4708 from SvenDowideit/sign-releases

Add md5 and sha256 to binaries on get.docker.io