Support for YubiHSM 2 as PKCS11 backend

[Michel Nederlof]

We're in the process of using the YubiHSM 2 [1] as a backend store for barbican.

It almost works, but it would need some small additions on the barbican code side to get it to work properly. We're working on that :)

Some caveats upfront:
- Minimal firmware version required: v2.3.1
  (otherwise the encrypt/decrypt methods are not available on the device [3])

Developers information can be found on yubico website [2]

[1] https://www.yubico.com/nl/product/yubihsm-2/
[2] https://developers.yubico.com/YubiHSM2/
[3] https://developers.yubico.com/YubiHSM2/Concepts/Capability.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/barbican/+/900107

[Josselin Mouette (jmouette)]

Thanks a lot for the patch. We are using YubiHSM as well and your work helped us immensely.

It was not entirely enough, though, which is why I’m proposing a small supplemental change.