Add tests for subpass dependencies

Add tests for subpass dependencies

New tests for external subpass dependencies between render pass
instances as well as implicitly added subpass dependencies. Tests
verify that the render passes are synchronized correctly using
external subpass dependencies. Also the conversion functions to
RenderPass/RenderPass2 are now implemented in vktRenderPassTestsUtil.

New tests:

dEQP-VK.renderpass*.subpass_dependencies.*

Components: Vulkan

VK-GL-CTS issue: 1143, 1148

VK-GL-CTS public issue: 97
Change-Id: Icc73a8cfc137ed6d64246c451cee1b1293c1d11b