Update help message for start-and-exit

  comment=STR           Write STR to the output

  script-debug          Debug this script itself

  timer                 Show test case execution time

  start-and-exit        Only initiate and start the "mysqld" servers, use the startup

  start-and-exit        Only initiate and start all servers, use the startup

                        settings for the specified test case if any

  start-dirty           Only start the "mysqld" servers without initiation

  fast                  Don't try to cleanup from earlier runs