Minor comment clarification (fixup)
Add tests for Krikri::Harvester#enqueue
Focus OAIHarvester#enqueue test on this class

Make the tests specific to this harvester type.  Other tests for
enqueue have been added to the Harvester spec.

This adds a test to ensure that harvest options particular to the
OAI type are saved correctly with the Activity.
Fix SoftwareAgent reporting of agent name

Make sure that classes extending SoftwareAgent and instances of
these classes can all report their agent name correctly.