Change DB connections to rely on tnsnames.ora

If able to read the tnsnames.ora file don't use the explicit connections. Needed for the switchover tests and also means we don't have to update when IT replaces machines. Tested as part of the ATLAS partition in M11, installed as a patch in: /sw/extras/sw_tmp/current/hlt/TriggerPanelSwitchOver cc ATR-24939 @cmerlass @astruebi @palacino @stelzer @ballbroo

Also replaced the popup from the Run3 schema check with a warning