[Executor] Add per-workload CGroup configuration
Created by: derkling
Reported by @deggeman
Currently we run all the workloads into the default CGroup defined by the test configuration. It should be possible to specify, for each workload, a cgroup to run it into. A proper check in the configuration file should be done to verify that the required CGroup exists in the current test configuration.
This missing feature could be correlated to: 73f20130 libs/wlgen/workload: move CGroup definition into run() method