Make gums-add-mysql-admin suitable for automated use (SOFTWARE-1577)

Update for gums-add-mysql-admin script.

See: https://jira.opensciencegrid.org/browse/SOFTWARE-1577

The latest build (gums-1.4.0-0.3.pre3) has this update as a patch, but maybe we can include it in the main sources for the next (pre)release...