Error Msg for missing db username & password  when installing

Added configurations for Mysql and Postgresql installers
to display an error message if user doesnt input a username to the
database username

Bug: 43528
Bug: 59663
Change-Id: Ib6b05d2d7e8ebb4438d3b0051c33d367f41a9957
Merge "Error Msg for missing db username & password  when installing"