rdbms: make LoadBalancer::reallyOpenConnection() handle setting DBO_TRX
Make LoadBalancer::reallyOpenConnection() handle initializing DBO_TRX
instead of Database::__construct().
- Avoid having the "catch" block appear like it returns a half-constructed Database.
- Use the variable name $conn instead of $db to be consistent throughout the class. Only send Database::__construct() parameters that it recognizes instead of mixing in setLBInfo() data.