Stack trace if SRC_DSN or DST_DSN is malformed

[tim-band]

Try setting SRC_DSN to postgres://localhost:5432/omop (instead of postgresql://...). Then run datafaker make-tables. You will get a stack trace. It would be better to output a friendly error report. This postgres: protocol is a common error issue. We could at least pick out the protocol and say that this is probably the cause of the issue.