Change default timeleft for igwn_auth_utils.find_scitoken

The igwn_auth_utils.find_scitoken function has a default timeleft value of 600 seconds. There was agreement in this thread that a lower value would be more appropriate, and that 60 seconds is likely the most sensible value.

Condor's default behavior renews tokens between 600 and 300 seconds before expiry. The default value of htgettoken's --minsecs option is 60.