Split descriptor set indexing render pass workload

Split descriptor set indexing render pass workload

The render pass workload for descriptor set indexing tests which call
DynamicBuffersInstance::iterate should be split into multiple
submissions to prevent timeouts observed in
dEQP-VK.descriptor_indexing.uniform_buffer_dynamic_in_loop
test.

A number (16) of command buffers, each for a separate render area, are
created and submitted separately.

Affects: dEQP-VK.descriptor_indexing*

Components: Vulkan

VK-GL-CTS Issue: 2061

Change-Id: Ib232854a1224aadbd63eaad30e15f893eeb48f85

Investigation for Khronos issue;
https://gitlab.khronos.org/Tracker/vk-gl-cts/issues/2061

Change-Id: Ib232854a1224aadbd63eaad30e15f893eeb48f85