just some feedback for those looking for an answer to this question. After some investigation, it appears IMO that the execution history plugin is not yet implemented for JBPM 5.0 or 5.1, although some execution history is available using BAM.
From what I've read, the JBPM project follows a phased approach, starting of with core features and adding features with subsequent releases, and I assume that this feature might be implemented in future, depending on the priority, if at all neccesary considering the planned BAM capabilities.
Please bear in mind that I am not an authority on this. this is merely an observation I am making.