Now we have two qcrypto backends, libiary-backend and afalg-backend,
but which one is faster? This patch add a cipher speed benchmark, it
helps us to measure the performance by using "make check-speed" or
using "./tests/benchmark-crypto-cipher" directly.

Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>