Support MySQL8 in test infrastructure

The testing infrastructure will be enhanced to support testing of versions of dependencies that are on the edge of support (see #1142 (closed)).

Setting up testing for MySQL is the focus of this issue.

In particular, We may need to adjust some of our test infrastructure for PHP <7.1.16 or PHP 7.2 less than 7.2.4 as per instructions at http://php.net/manual/en/ref.pdo-mysql.php .