fix self checks so yubihsm is optional

[jas4711]

There ought to be some self checks that could be run without a yubihsm

[fredrikt]

Funny, I was just about to propose that since I've put python-pyhsm in a CI system now =)

See this commit https://github.com/SUNET/VCCS/commit/ad98ef6ef4c65d8bf92e1b77923b4159473ff914 as inspiration.

/Fredrik