Fail test.php when phpunit.phar cannot connect to the database

[danielbachhuber]

When test.php cannot connect to the database, we're currently producing this error message:

Instead, we should fail test.php early and return an error code.

From https://travis-ci.org/pantheon-systems/wordpress-unit-tests/builds/276388655

[danielbachhuber]

Needs to be fixed upstream: https://core.trac.wordpress.org/ticket/41916