This changeset provides simple tls support for a registry instance. Simply
providing a cert and key file are enough to get a tls registry running. If the
certs are trusted by the client, tls can be used throughout the push and pull
process.
If more complex TLS options are required, it is recommend that a proxy be used.
Contributions will be accepted to add more features, if necessary.
Signed-off-by: Stephen J Day <stephen.day@docker.com>