workload: add possibility to set pauses before and after executing a workload

Created by: mdigiorgio

By means of a start and an end pause parameter it is now possible to set a period of time to wait after starting collecting traces and before the execution of workload (for example to allow something to settle down). In addition, you can also set a period of time to wait after the workload has executed and before stopping the trace collection.

The two parameters are optional and their default value is zero.

Signed-off-by: Michele Di Giorgio michele.digiorgio@arm.com