MFC r294894:

Adjust vm.max_wired in order to avoid hitting EAGAIN artificially

Set vm.max_wired to INT_MAX in :mlock_err, :mlock_mmap, and :mlock_nested to
avoid hitting EAGAIN artificially on the system when running the tests

Require root privileges in order to set the sysctl

Add allow_sysctl_side_effects to require.config as this test is now adjusting
sysctls that can affect the global system state

Unlike the version submitted by cem in OneFS, this version uses a scratch file
to save/restore the previous value of the sysctl. I _really_, _really_ wish
there were better hooks in atf/kyua for per test suite setup/teardown -- using
a file is kludgy, but it's the best I can do to avoid situations where (for
instance), sysctl(3) may fail and drop a core outside the kyua sandbox.

Based on a patch submitted by cem, but modified to take business logic out of
ATF_TP_ADD_TCS(3).