Fix cpuhp test

Created by: qperret

The CPU hotplug test is full of useless dependencies which silently talk to the target (rt-app, freezing userspace, ftrace, ...). When the target crashes during the hotplug stress, requests sent to the target because of the above modules can hang indefinitely, or fail miserably. That is an issue since, in the specific case of the hotplug test, we would like to classify these crashes as test failures.

Remove all the dependencies by overwritting the runExperiments method of LisaTest in order to avoid using an Executor. The test spawns a bash script on the target that plugs CPUs in and out, and does nothing on the host side during a (configurable) amount of time before checking if the target is alive.