credential: follow Person_generatePassword API change

This script no longer allow to control the number of letters and digit
3 jobs for for_testrunner_1 in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner1

00:42:52

passed ERP5.PerformanceTest-TestRunner1

00:32:15

failed ERP5.UnitTest-TestRunner1

01:18:06