support ignore-table option

[bomoko]

Hi all,

When plugging this into drush sql-dump I saw that we needed the ignore-table option (see https://dev.mysql.com/doc/refman/5.7/en/mysqldump.html#option_mysqldump_ignore-table).

Currently we're following the mysqldump-php convention of "exclude-tables", but that doesn't seem to be a mysqldump option, so I suggest we swap out one with the other.