MFC r335287, r335290

r335287:
praudit(1): return 0 on success

Cherry pick https://github.com/openbsm/openbsm/commit/ed83bb3

Submitted by: aniketp
Reviewed by: rwatson, 0mp
Obtained from: OpenBSM
Sponsored by: Google, Inc. (GSoC 2018)
Pull Request: https://github.com/openbsm/openbsm/pull/32

r335290:
praudit(1): add tests

Submitted by: aniketp
X-MFC-With: 335287
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15751