Fix tests that enable depth testing on undefined depth buffer

Fix tests that enable depth testing on undefined depth buffer

There are tests in the load_store_op_none category set up like this:

Depth load: NONE
Depth store: NONE
Depth testing: ON
Depth op: GREATER
Depth write: OFF

This configuration is bogus because the depth buffer will be
undefined as this particular test won't initialize the render
area inside the render pass and it enabled depth testing
with a comparison function that depends on the contents of the
depth buffer.

Fix it by detecting this scenario and making the depth comparison
ALWAYS to ensure that depth testing doesn't drop any samples,
which is what the test expects.

Affects:
dEQP-VK.*.load_store_op_none.depth*

Components: Vulkan
VK-GL-CTS issue: 4209

Change-Id: Icab24dcf7f46156b7b59541ea64e5823deec53d1