clusterbuster: support heterogeneous workloads

[amorenoz]

Depending on the configuration, different types of stressors might end up competing for the same resources. For example, if PAO (Performance Add-on Operator) is used on a cluster, kubelet and openvswitch are pinned to the same CPUs.

Being able to generate an heterogeneous, realistic workload (e.g: combination of network load and k8s control plane tasks) would be a very good way of testing how this resource sharing affect the overall cluster scalability.