Added a new KernelTestBase build upon PHPUnit

As part of the modernization strategy of the test infrastructure #2304461: KernelTestBaseTNG™ changes KernelTestBase to leverage phpunit instead of simpletest as testing base.

This has several advantages, pretty much the same ones like phpunit has, like better tool support.

In order to change your kernel test to use the new infrastructure you need to take the following steps:

Conversion

Note: Until Drupal 8.0.x just straight conversions are allowed to land in core itself. What are straight conversions. Straight conversions are conversions
that just change the base class

• Extend from \Drupal\KernelTests\KernelTestBase instead of \Drupal\simpletest\KernelTestBase
• Use a new place for the tests:
  

  rename from core/modules/system/src/Tests/Extension/ModuleHandlerTest.php
  rename to core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
  

  And update the namespace accordingly:

  -namespace Drupal\system\Tests\Extension;
  +namespace Drupal\Tests\system\Kernel\Extension;
  

• (optional) Move the assertions from simpletest to phpunit ones, see RandomGeneratorTrait as a mapping
• Use settingsSet() to setSettings()
• Use register() instead of containerBuild

Run the kernel tests using phpunit

$ cd core
$ export SIMPLETEST_DB=mysql://root:@localhost/dev_d8; ./vendor/bin/phpunit --testsuite=kernel