Adding WordPress-Tests checkout.

Added a checkout of WordPress-Tests to /vagrant/www/wp-tests and the tests configuration file to /vagrant/www/wp-tests/wp-tests-config.php.

phpunit is now installed on the vm for executing tests.

Added a `wptests` database with a matching `wptests` user to access it.

Added the environment var `WP_TESTS_DIR` to /etc/environment (using init.pp).

Closes #71
Replaced spaced indentation with tabbed indentation.
Updating HACKING.md file with the new www/wp-tests dir.

HACKING.md describes important directories in Quickstart, adding the
new wp-tests dir to it.
Updating README.md with instructions for testing

Added instructions for unit testing via `phpunit` and `wp-tests`. 

Added a link to the documentation for WordPress-Tests.

Added phpunit and WordPress-tests to the list of things you get in VIP Quickstart.
Merge pull request #108 from Mobius5150/master

Add WordPress-Tests checkout