This helper function behaves similarly to co_sleep_ns(), but the
sleeping coroutine will be resumed when using qemu_aio_wait().

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Tested-by: Liu Yuan <namei.unix@gmail.com>
Reviewed-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>