Fix image layouts in descriptor indexing tests

Fix image layouts in descriptor indexing tests

This is a fix for regression introduced in 4301d73b3
- in fact this is a partial revert of that change.

After 4301d73b3, the current image layout (READ_ONLY_OPTIMAL) was
different than image layout used in descriptor set bindings
(GENERAL), what is invalid.

As some of these descriptor set binding are used for STORAGE_IMAGEs,
which require images in GENERAL layout, the simplest fix was to revert
back to using GENERAL layouts.

Components: Vulkan

VK-GL-CTS Issue: 1881

Change-Id: Idac940135bafe6be6e456d0ec554d5cc3c3fc8e7
Affects: dEQP-VK.descriptor_indexing.*