Sum well rates in computeWellRatesWithBhp for distributed wells.

This needs summation over all procs that share the well as it needs
information from all perforations. Some of them might reside on other
processes.

opm/simulators/wells/StandardWell_impl.hpp

@@ -2562,6 +2562,7 @@ namespace Opm
                 well_flux[ebosCompIdxToFlowCompIdx(p)] += cq_s[p].value();
             }
         }
+        this->parallel_well_info_.communication().sum(well_flux.data(), well_flux.size());
     }