Enable automatic NUMA balancing on lizard

After reading chapter 8 on https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html-single/Virtualization_Tuning_and_Optimization_Guide/index.html#sect-Virtualization_Tuning_Optimization_Guide-NUMA-Auto_NUMA_Balancing and other Red Hat performance tuning doc, I came to the conclusion that we should enable automatic NUMA balancing on lizard (echo 1 > /proc/sys/kernel/numa_balancing, i.e.
sysctl::value { 'kernel.numa_balancing': value => 1 }).

It is supposed to give us better performance, and the other options are not practical:

manual NUMA tuning: quite some initial + maintenance work, let’s avoid this if we can
numad: the package is in Stretch but not in Jessie, and according to Red Hat it’s not really more efficient than automatic NUMA balancing

To be able to evaluate how well this works, we can:

benchmark
use numastat -c qemu-system-x86_64, that gives per-command information, so we can easily check what CPUs our kvm processes are using; see 8.3 on https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html-single/Virtualization_Tuning_and_Optimization_Guide/index.html)

Original created by @intrigeri on 11179 (Redmine)

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