TRUNK-6343: Add PostgreSQL support to the simple setup in the setup wizard (#5040)
* TRUNK-6343: Add PostgreSQL support to simple setup in the setup wizard
* Add user interface changes
* add postgres as the default superusername
* remove code duplication
* handle when a user or a dbname already exists
* fix the create statement
* fail gracefully
* improve logging
* remove checks for existing db users and name for postgres
