STYLE: use Time::printExecutionTime() method

- makes format of ExecutionTime = ... output configurable (#788)
  and reduces code clutter.

applications/utilities/postProcessing/optimisation/computeSensitivities/computeSensitivities.C

@@ -64,9 +64,7 @@ int main(int argc, char *argv[])
         }
     }
 
-    Info<< "ExecutionTime = " << runTime.elapsedCpuTime() << " s"
-        << "  ClockTime = " << runTime.elapsedClockTime() << " s"
-        << nl << endl;
+    runTime.printExecutionTime(Info);
 
     Info<< "End" << endl;