Add --deqp-validation=enable/disable option

Add --deqp-validation=enable/disable option

Specifying --deqp-validation=enable when running Vulkan tests will
result in:

1) vkt::TestCaseExecutor will create debug report callback on default
instance. Any debug messages reported during test execution will be
included as a separate log section in the test log.

2) vkt::Context will enable known validation layers on both default
instance as well as default device.

If any errors are reported (for example validation errors) test result
will be set to InternalError.

Change-Id: Icc89a3f57f0c19170988d7b518fe6b24dcf3df6e