Testcase: PS Mem fetch without output with smaller textures.

[RenfengLiu]

Using Knob fullscreen-quads-texture-path to switch between texture files, available files are

 "benchmarks/textures/tiger_1x1.jpg"
 "benchmarks/textures/tiger_591x720.jpg"
 "benchmarks/textures/tiger_1182x1440.jpg"
 "benchmarks/textures/tiger_2364x2880.jpg"

Full knob list:

{
    "deterministic": true,
    "enable-skybox": false,
    "enable-spheres": false,
    "enable-metrics": false,
    "fullscreen-quads-count": 1,
    "fullscreen-quads-type": "Texture",
    "fullscreen-quads-single-renderpass": true,
    "vs-alu-instruction-count": 100,
    "texture-count": 2,
    "disable-ps-output": true,
    "fullscreen-quads-texture-path": "benchmarks/textures/tiger_2364x2880.jpg"
}