This PR makes restores the pre-Docker 1.10 behavior of allowing
uppercase characters in registry hostnames.
Note that this only applies to hostnames, not remote image names.
Previous versions also prohibited uppercase letters after the hostname,
but Docker 1.10 extended this to the hostname itself.
- Vendor updated docker/distribution.
- Add a check to "normalize" that rejects remote names with uppercase
letters.
- Add test cases to TestTagValidPrefixedRepo and
TestTagInvalidUnprefixedRepo
Fixes: #20056
Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
