Added random generator utility methods via new RandomGeneratorTrait.
Updated extension/config/schema test helper methods for PHPUnit.
DrupalKernel::setContainer() should be compatible with ContainerAwareTrait.
Fixed DependencySerializationTrait breaks if there is no container.
Added missing TestBase methods.
Added second Kernel test suite.
Fixed various kernel tests.

- Test class properties must be declared.
- Non-existing modules cannot be enabled.
Removed $configDirectories. (to be reimplemented as opt-in)
Fixed error handling for non-existing public static $modules.
Fixed precompiled container leaks into tests.

See https://github.com/symfony/symfony/pull/11422
Performance: Only use precompiled container if there are > 1 test methods.
Added Travis-CI configuration. Limited to unit tests.