improvements on database setup

• Tired of seeing no such file or directory on ls -al /etc/redhat-release when running on Debian. Let's please hide that error.
• Tired of seeing cannot create user keauser. It happens because the DROP before it operates on the wrong user.
• Let's make PostgreSQL setup consistent with MySQL.
  • DROP first, CREATE after.
  • assert result.succeeded on all statements.
  • DROP DATABASE IF EXISTS