tools: hv: add vmbus testing tool

This is a userspace tool to drive the testing. Currently it supports
introducing user specified delay in the host to guest communication
path on a per-channel basis.
Signed-off-by: Branden Bonaby <brandonbonaby94@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>