Fix regression in dEQP-VK.pipeline.multisample.sample_mask

Fix regression in dEQP-VK.pipeline.multisample.sample_mask

The commit 83f7fcd8 introduced two ways of downloading
rendered images from device (RESOLVE or COPY_SAMPLES).

All previously existing tests should continue to use RESOLVE mode, as
the new COPY_SAMPLES mode changes the behavior of MultisampleRenderer
class (and requries additional set of shaders).

Affects:
dEQP-VK.pipeline.multisample.sample_mask*

Components: Vulkan

VK-GL-CTS issue: 676

Change-Id: I0c59cf0b4c9734c982b78606dc3cc9d1d721b547
(cherry picked from commit e3b288e22f038449559f2ccaa4825856ef729fce)