Folding slon.stop() and coordinator.join(slon) into one loop.

Stopping the slons and joining their processes in separate
loops apparently can cause the regression test to hang under
some rare race conditions.

clustertest/regression/common_tests.js

@@ -70,8 +70,6 @@ function launch_slon(coordinator) {
 function terminate_slon(coordinator) {
 	for(var idx=0; idx < slon_array.length; idx++) {
 		slon_array[idx].stop();		
-	}
-	for(var idx=0; idx < slon_array.length; idx++) {
 		coordinator.join(slon_array[idx]);		
 	}
 }