revocation_endpoint only works with JWT Tokens

[schlenk]

The oic.extensions.provider revocation endpoint tries to load the details of the token to revoke and fails to revoke it, if it is not an JWT token. RFC 7009 does not demand the format of the token to be JWT.

At first, the get_info call will fail, because DefaultToken does not implement it:
https://github.com/OpenIDC/pyoidc/blob/64c5e3b6c099496787093a778fbc8b0d7e044e1d/src/oic/extension/provider.py#L776

And even if that works, the token_access method will block the revocation, as it requires JWT attributes:
https://github.com/OpenIDC/pyoidc/blob/64c5e3b6c099496787093a778fbc8b0d7e044e1d/src/oic/extension/provider.py#L720