Provide more information about invalid tokens
We now include an "errors" field in the JSON data returned that specifies
the reason why the token is invalid (entirely invalid, expired, missing
ACLs).
Unit-tests are also adjusted for this.
Fixes https://pagure.io/pagure/issue/4307
Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr></pingou@pingoured.fr>