use waitForAutoscalingInstances instead of sleep

Change-Id: I3fb5adea480f58762c9ce0eca6cdc343c20c02b3
diff --git a/cloud-deploy-pipeline.groovy b/cloud-deploy-pipeline.groovy
index f1476f8..75c345b 100644
--- a/cloud-deploy-pipeline.groovy
+++ b/cloud-deploy-pipeline.groovy
@@ -228,7 +228,7 @@
                             aws.updateAutoscalingGroup(venv_path, env_vars, scaling_group, ["--desired-capacity " + STACK_COMPUTE_COUNT])
 
                             // wait for computes to boot up
-                            sleep(120)
+                            aws.waitForAutoscalingInstances(venv_path, env_vars, scaling_group)
                         }
 
                         orchestrate.installKubernetesCompute(saltMaster)