[ENV-429] Revert to previous step submission concurrency model (#299)

core/src/main/java/com/cloudera/labs/envelope/run/Runner.java

@@ -284,6 +284,10 @@ else if (step instanceof TaskStep) {
         LOG.debug("Finished looking into step: " + step.getName());
       }
 
+      // Wait for the submitted steps that haven't yet finished
+      awaitAllOffMainThreadsFinished(offMainThreadSteps);
+      offMainThreadSteps.clear();
+
       // Add all steps created while looping through previous set of steps.
       steps.addAll(newSteps);
 
@@ -303,14 +307,8 @@ else if (step instanceof TaskStep) {
             "that do not exist. Steps: " + steps);
       }
       previousStepStates = stepStates;
-
-      // Avoid the driver getting bogged down in checking for new steps to submit
-      Thread.sleep(20);
     }
 
-    // Wait for the submitted steps that haven't yet finished
-    awaitAllOffMainThreadsFinished(offMainThreadSteps);
-
     LOG.debug("Finished batch for steps: {}", StepUtils.stepNamesAsString(steps));
   }