Tests for console commands

Summary:
The kernel test checks if every command in app/Console/Commands/ is
also declared app/Console/Kernel.php $commands array (or otherwise
added to the console kernel).

The TestCase class provides logic specific to test commands: it
resolves the command and gets a Symfony command tester instance.

We give a sample of how to implement a test class for a command in
InspireTest, which tests the Laravel default command inspire.

Reference: http://symfony.com/doc/current/components/console/introduction.html#testing-commands

Test Plan: Run tests

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D240