#8 startup does not work when some cached authority key certificates are not valid anymore

[Tobias Boese]

When the authority keys are expired in the cache they are just skipped and not refetched.

when a key is expired we need to refetch it. (currently we just ignore and skip it)
this leads to an endless loop where we want to fetch the consensus document and try to validate it but dont have enough keys from the authorities.

Workaround : delete st-* files in temp folder (especially : st-authority-key-certificates.txt)