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
MFC after: 2 weeks
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15898