[ENSCORESW-665]. Making sure we report the correct DBI error.

It seems that $DBI::errstr has a very strange life. We can get the error message
recived by incorrect connections or bad drivers (DBD::mysql is missing) when we
just warn the error. However concatenating it into another string makes the
message disapear. Even assignment and then concat will not work. Instead we
have switched to using the $@. This has the error in it.