Overhaul code to read old GCE credential file format. #6657
Overhaul code to read old GCE credential file format. #6657

When a credentials file has info for multiple GCE accounts, information
from only one account is used, and which account can be specified (like
when reading the new sql file format).
Also, restore detection of incomplete credential data.

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor