support setting (custom) jdbc driver properties in config

this let's us (programmatically) hand tune the properties before connecting

please review and let me know if there's anything I assumed/did that seems wrong ...

the second commit makes sure only `SQLException`s from connect are wrapped.
I do find this desirable since runtime Java exceptions thrown by the driver might get swallowed without any useful info e.g. I got a NPE from the MySQL driver when passing invalid properties which ended up as a (confusing) JDBCError with *"The driver encountered an unknown error: "* !