vhost-user-test: wrap server in TestServer struct In the coming patches, a test will use several servers simultaneously. Wrap the server in a struct, out of the global scope. Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Thibaut Collet <thibaut.collet@6wind.com>