tests: Segregate positive LVT tests
tests: Segregate positive LVT tests

Created new test class (VkPositiveLayerTest) for positive tests,
moved existing positive test into this class and split tests having
a mix of positive and negative tests. This should make things a bit
cleaner when adding valid usage IDs and adding test names into the
VU database.  In the future the class can be extended to do error
checking automatically.

Change-Id: I33af3d80f154b55bb55ad0c0e515a773b144c701

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers