[FEM] Elmer: fixes for multi-threading

- load the results depending on the used cores, not always the multi-thread results
- avoid unnecessary console output - this info is already output in tasks.py
- handle number of cores as int to save in total 2 conversions

src/Mod/Fem/femsolver/settings.py

@@ -116,10 +116,6 @@ def get_cores(name):
     """
     if name in _SOLVER_PARAM:
         cores = _SOLVER_PARAM[name].get_cores()
-        FreeCAD.Console.PrintMessage(
-            "Number of CPU cores to be used for the solver run: {}\n"
-            .format(cores)
-        )
         return cores
     else:
         FreeCAD.Console.PrintError(
@@ -244,7 +240,7 @@ class _SolverDlg(object):
         return the_found_binary
 
     def get_cores(self):
-        cores = str(self.param_group.GetInt("UseNumberOfCores"))
+        cores = self.param_group.GetInt("UseNumberOfCores")
         return cores
 
     def get_write_comments(self):