Use global variable

One of the variables in a function exported to GNU Parallel was not
itself exported.  Pathing woes ensued.

Signed-off-by: Alex Nelson <a.nelson@prometheuscomputing.com>
(cherry picked from commit ad80d816f71144e1cee6261e4e35e10f662da060)

Fixed one additional variable misname in the error counting function.

Conflicts:
	src/do_difference_workflow.sh