ref_vk: add more debug around VULKAN_SDK for CI

ref_vk/wscript

@@ -32,6 +32,8 @@ def configure(conf):
 			conf.error('VULKAN_SDK environment variable is not available, ref_vk will not be built')
 			conf.end_msg('no')
 		conf.env.VULKAN_SDK = conf.environ['VULKAN_SDK']
+		if not os.path.isdir(conf.env.VULKAN_SDK):
+			conf.error(conf.env.VULKAN_SDK + ' is not a valid directory')
 		conf.end_msg('found at ' + conf.env.VULKAN_SDK)
 
 	conf.load('glslc')

scripts/build_windows_engine.sh

@@ -3,6 +3,10 @@
 . scripts/lib.sh
 
 export VULKAN_SDK=C:/VulkanSDK/$VULKAN_SDK_VERSION
+ls -la C:/
+ls -la C:/VulkanSDK
+ls -la $VULKAN_SDK
+ls -la $VULKAN_SDK/Bin/glslc.exe
 
 # Build engine
 cd $TRAVIS_BUILD_DIR