workloads: port shellscript workload from WA2
workloads: port shellscript workload from WA2

Port shellscript workload that allows running an arbitrary shellscript
as a WA workload from WA2.

lisatn/workload-automation,ARM-software/workload-automation,ARM-software/workload-automation,setrofim/workload-automation,lisatn/workload-automation,lisatn/workload-automation,lisatn/workload-automation,ARM-software/workload-automation,ARM-software/workload-automation,setrofim/workload-automation,setrofim/workload-automation,setrofim/workload-automation