fix loading instance in waitForAutoscalingInstances

Change-Id: I70aa8f33cb363a7e2a819a13371e3dd10b1d936e
diff --git a/src/com/mirantis/mk/Aws.groovy b/src/com/mirantis/mk/Aws.groovy
index a016e13..acc33d7 100644
--- a/src/com/mirantis/mk/Aws.groovy
+++ b/src/com/mirantis/mk/Aws.groovy
@@ -177,7 +177,7 @@
                 // get instances in autoscaling group
                 def out = aws.describeAutoscalingGroup(venv_path, env_vars, group_name)
                 print(common.prettyPrint(out))
-                def instances = out['AutoScalingGroups'][0]['Instances']
+                def instances = out['Instances']
 
                 // check all instances are InService
                 if (common.countHashMapEquals(instances, 'LifecycleState', 'InService') == 0) {