autotest: tidy WheelEncoders test
autotest: rover: tidy PolyFenceObjectAvoidance code
autotest: add load_fence_using_mavwp
Also corrects the mission item types being returned by the mission-item-to-misison-item-int converter
autotest: fix Rover PolyFenceAvoidanceBendyRulerEasier test
these tests weren't being run becausethey were disabled based on support for loading fence items from QGC files.
autotest: fix Rover PolyFenceAvoidanceBendyRuler test
Peter Barker