Turn on vk unit tests

* Degrade error when changing the rendering backend from Properties to
no longer be fatal.
* Support using a single graphics queue for the Vulkan backend. Cloud
devices only support a single queue and some Vulkan implementations such
as Swiftshader expose only one queue for simplying their implementation,
so we'll need to support one.

Bug: 175618060
Bug: 162628999
Test: hwui_unit_tests
Test: experiment on Pixel 4 enforcing a single queue (settings app,
maps, sysui)

Change-Id: I495fcabc3c89bd62bbb833998eab4944c6660f6f