This allows hostnames to contain uppercase characters, matching behavior
in Docker versions before 1.10. It does not attempt to canonicalize
hostnames into a lowercase format before parsing, since this could lead
to corner cases (for example, making Hostname.Domain.Com/ref ambiguous
on a daemon which contains references for both hostname.domain.com/ref
and Hostname.Domain.Com/ref).
Fixes: #1433
Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
950d34d210