speedometer: fix @once methods which declare attributes
speedometer: fix @once methods which declare attributes

We need to make those attributes class-attributes, to make sure they are still
defined in subsequent jobs. We still access them through 'self', however.

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