Make MySQLPDOTest::extractVersion() more liberal

Make MySQLPDOTest::extractVersion() more liberal

MySQL/MariaDB version strings may have suffixes which may contain dots;
for instance, Debian stretch has 5.5.5-10.1.37-MariaDB-0+deb9u1 or
such.  Therefore, we make the version extraction more liberal, and only
require that there are at least three parts separated by dot, and
ignore additional parts.

We also fix an erroneous test expectation, which would be triggered on
CI now, right away.  This patch has been provided by petk@.