Decouple VulkanManager from RenderThread

This CL allows for more than one VulkanManager to exist.
VulkanManager ctor are public allowing for classes other
than RenderThread to instantiate it.
Secondary VulkanManager can be used to render on a thread
other than RT.

Test: Ran HWUI unit tests and several apps
Change-Id: Ibfd76c86ff67e01617a500902bba7431b928f5c0