Issue #2610858 by cilefen, ravi.shankar, Cameron Tod, shubham.prakash, joachim, mohit_aghera, Madhura BK, kostajh, asvira, vacho, Grevil, daffie, dawehner, mradcliffe: Add informative error message for 'Connection refused' errors in MySQL

Issue #82571 by asvira, Gogowitsch, flk, tstoeckler: Error message in installer mentions possibly wrong username, etc. but not port