Enable random writes for storage texel buffers

Enable random writes for storage texel buffers

In the descriptor set random tests, enable random writes when the
descriptor type is a storage texel buffer.

In addition, this commit fixes a problem with storage image barriers.

Affected tests with random writes:
dEQP-VK.binding_model.descriptorset_random.*outimgtexlow*
dEQP-VK.binding_model.descriptorset_random.*lowimgsingletex*
dEQP-VK.binding_model.descriptorset_random.*storageimghigh*

Affected tests:
dEQP-VK.binding_model.descriptorset_random.*

VK-GL-CTS issue: 1973
Components: Vulkan

Change-Id: I5a407ebc239cca48cee56c5901f45bd4118b3c3b