Fix Nusselt number for the overlapping bc_ids case
Fix Nusselt number for the overlapping bc_ids case

I noticed this when working on the ParsedBoundaryQoI code.  libMesh
boundaries can have multiple ids, and we might specify those ids in
the qoi, and if we do then we probably don't want to double-count
contributions from the overlapping boundary region.

nicholasmalaya/grins,vikramvgarg/grins,nicholasmalaya/grins,nicholasmalaya/grins,cahaynes/grins,vikramvgarg/grins,cahaynes/grins,cahaynes/grins,vikramvgarg/grins,cahaynes/grins,vikramvgarg/grins,vikramvgarg/grins,cahaynes/grins,cahaynes/grins,nicholasmalaya/grins,vikramvgarg/grins