KEYRING ccache can hide valid tickets when it contains expired ticket

[Greg Hudson]

> I'm trying to use KEYRING as default ccache and noticed that when there is a
> service ticket expired, `klist` would truncate the list of available tickets
> in my ccache with an error message:
> 
> klist: No credentials cache found while retrieving a ticket

Thanks for investigating and reporting this bug.  I confirmed that I can 
reproduce the error (using kvno on a server principal created with 
-maxlife 1m) and filed a PR to fix it:

https://github.com/krb5/krb5/pull/1546