Fix upgrade 2 10

I ran into a issue where i had rows that were null, this in turn made the upgrade script fail.  I was upgrading from 2.05

Note: this pull request replaces my other issue with the same solution
Can you replace this line with this query instead?

    DELETE FROM nt_nameserver_log WHERE output_format NOT IN ('tinydns','djb','nt','bind') OR output_format IS NULL;