MFC r335792, r336564, r336579

r335792:
audit(4): add tests for several more administrative syscalls

Includes ntp_adjtime, auditctl, acct, auditon, and clock_settime. Includes
quotactl, mount, nmount, swapon, and swapoff in failure mode only. Success
tests for those syscalls will follow. Also includes reboot(2) in failure
mode only. That one can't be tested in success mode.

Submitted by: aniketp
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15898

r336564:
Separate the audit(4) tests for auditon(2)'s individual commands

auditon(2) is an ioctl-like syscall with several different variants, each of
which has a distinct audit event. Write separate audit(4) tests for each
variant.

Submitted by: aniketp
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D16255

r336579:
audit(4): add more test cases for auditon(2)

auditon(2) is an ioctl-like syscall with several different variants, each of
which has a distinct audit event. This commit tests the remaining variants
that weren't tested in r336564.

Submitted by: aniketp
X-MFC-With: 336564
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D16381