In order to avoid cloud-hypervisor to rely on a pending PR for the empty
crate "vhost", this commit temporarily copies the content of the crate
based on branch jiangliu/v1 18b5081d9199c76eca49da1971c9d1a65e53e5ff.
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>