During the "Post Install" via the wizard, after entering a "MySQL Root Password" into the form, then clicking submit, the error is produced:
DBI connect failed: Access denied for user 'root@localhost' (using password: NO)
*** This issue has been around for a while. It seems either something about CentOS 7 or the Virtualmin Installer is having a problem. ***
The issue above causes the Virtualmin Installer NOT to delete "test" database, or remove the "anonymous" user accounts which then need to be performed manually.
Clicking the button to return to the previous page does produce a form field which now has the new password. After this, the install process completed successfully through the remaining steps.
*** ClamAV is the only other error during the install, but this is a known issue with a workaround available ***