audit(4): add tests for access(2), chmod(2), and friends

access(2), eaccess(2), faccessat(2), chmod(2), fchmod(2), lchmod(2), and
fchmodat(2).

Submitted by: aniketp
MFC after: 2 weeks
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15805
Differential Revision: https://reviews.freebsd.org/D15808