Fix UTF-8 data in test_reports table

[preaction]

For the longest time, CPAN Testers has not supported UTF-8 data. This has resulted in some interesting problems, not the least of which is that Andreas König and Slaven Rezić both have to encode their name with HTML escapes (ö and ć respectively).

The correct solution is for the test report data to be stored in a utf8mb4 column in MySQL. We need to modify the test_reports table to be fully utf8mb4 throughout.

To get there from here will take some doing, though: With 12,000,000 records, this will take some time. We need to minimize downtime, so we may need to migrate in stages: The first stage to migrate most of the reports to a new table, then turn off incoming reports, then migrate the the rest of the reports to the new table, then rename the tables.

[preaction]

Fixing this will allow us to start adding better indexes to this table. Right now, I'm generating a column for the tester e-mail address, but when I add an index MySQL complains that the data is not valid for the character set, no matter which character set I use...