Changed the command pool management

Changed the command pool management

> The Vulkan::Graphics class manages all command pools.
> Creation of command pools is no longer exposed.
> Command pools are lazily created when command buffer creation is required and are stored in a map using the calling thread's ID as the key.
> All the command pools allocated by the Vulkan::Graphics class are using the eResetCommanBuffer flag to allow for explicit command buffer resetting.

Change-Id: I92a275cf591b3a85c98d596f977b9ec4ef4211c6