wp-now: Support running integration tests

[GaryJones]

The regular install-wp-tests.sh found with most plugins uses/requires a MySQL setup. It would be great to be able to have a playbook for how to allow plugins to run their integration tests with wp-now. For example:

cd MyPlugin
composer install
composer test-integration (or wp-now --tests, etc.)

This may fall more on the sqlite database plugin side of features, but being able to have the same setup for testing as what the plugin could be running in the wild with (and locally) seems advantageous.

[danielbachhuber]

Great idea!

We might need to sort out WordPress/wordpress-playground#594 first.