Run the plain SHA digest tests from NIST.

Pass in an explicit digest length to the Crypto constructor since it
was assuming only sessions with a MAC key would have a MAC. Passing
an explicit size allows us to test the full digest in HMAC tests as
well.

Reviewed by: cem
MFC after: 1 month
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D19884