Use helper functions stack_suspend and stack_resume

These wait for the stack state to get to complete,
this wasn't done consistently. In test_autoscaling we were
only waiting for the resource state to get to SUSPEND_COMPLETE
and this lead to a time sensitive bug.

Change-Id: Id985d833dc0b4cab1e3cb9d8f67d5d8cc94b5863
Closes-bug: #1438717
diff --git a/functional/test_aws_stack.py b/functional/test_aws_stack.py
index 5aabe95..d8ba937 100644
--- a/functional/test_aws_stack.py
+++ b/functional/test_aws_stack.py
@@ -203,11 +203,5 @@
         url = self.publish_template(self.nested_name, self.nested_template)
         self.template = self.test_template.replace('the.yaml', url)
         stack_identifier = self.stack_create(template=self.template)
-
-        self.client.actions.suspend(stack_id=stack_identifier)
-        self._wait_for_resource_status(
-            stack_identifier, 'the_nested', 'SUSPEND_COMPLETE')
-
-        self.client.actions.resume(stack_id=stack_identifier)
-        self._wait_for_resource_status(
-            stack_identifier, 'the_nested', 'RESUME_COMPLETE')
+        self.stack_suspend(stack_identifier)
+        self.stack_resume(stack_identifier)