Fix cmake warnings

Fix cmake warnings

Running cmake command under Windows as

cmake -G "Visual Studio 12 Win64" /path/to/vk-gl-cts

or

cmake /path/to/vk-gl-cts

there are policy warnings CMP0054 stating:
"Only interpret if() arguments as variables or keywords when unquoted"

Fix: remove unnecessary quoting at complaining lines.
Also do not use dereferencing (i.e. ${var}) on variable due to cmake
does dereferencing automatically on variables in if statement. Good
explanation is at https://stackoverflow.com/questions/25809332/

Components: Framework

VK-GL-CTS issue: 492

Change-Id: I5258f4a5145588efb34ba2356ba25004277f9213