Make AFS check regex more generic

[mesmith75]

The regex to parse the output of tokens is here: https://github.com/ganga-devs/ganga/blob/develop/ganga/GangaCore/GPIDev/Credentials/AfsToken.py#L29

It is not generic enough as someone has a command that returns:

Tokens for [email protected] [Expires Jan 24 18:13]
   --End of list--

It would be good to try and get away from this if we can.