This is because the server handles the timestamp key and timestamp signing.
So there can only ever be 1 key. Thanks @mtrmac for pointing this out.
This change also refactors some of the test code somewhat.
Signed-off-by: Ying Li <ying.li@docker.com>
If the client sends a root.json with an invalid timestamp key ID,
possibly because they are pushing an existing repo to a new server,
then the server should reject the update.
Signed-off-by: Ying Li <ying.li@docker.com>