If mysqlclient has been compiled against a vulnerable version of
libmysqlclient then this test will fail. There is overlap between this
and our custom Django system check for ensuring mysqlclient has been
compiled against libmysqlclient >= 5.7.11, however there advantages in
having both:
* the system check is run during deploy, unlike this test
* however this test is more thorough since it actually checks TLS
behaviour and not just version numbers (but this method cannot be used
in the system check run during production deployment, since it relies on
having a MySQL server instance that doesn't support TLS, to emulate the
TLS being stripped by an attacker)