numatune: Check for required utility

The test liberally uses the 'numactl' utility, but does not first
verify that the tool exists resulting in FAIL's rather than SKIP's.
Don't assume control groups active

The test as written assumes control groups are active, thus when attempting
to stop and restart things don't necessarily go 'as expected'.  Furthermore,
the failure path where different results are expected when stopped won't be
a failure resulting in a test FAIL that isn't valid.

Modify the test such that when it's stopping control groups - keep track
of whether they were started before stopping, then in the methods to
{set|get}_numa_parameters() add a check in the expected failure path to
not FAIL the test if cgroups were not stopped.

Adjust the libvirtd restart logic a bit since that restart is only
necessary if control groups were stopped.

Swap order to finally to restore guest state as the libvirtd restart
can fail/except thus we wouldn't have restore the guest leading to
potential other problems.

Signed-off-by: John Ferlan <jferlan@redhat.com>