tests: Fix layer path
tests: Fix layer path

The wrapping test could silently fail if the layer path wasn't set.

Change-Id: I6a8fae3da0e88281f346b8eb8aa4b762b149a785

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