Merge pull request #930 from hjydxy/memory_sw_limit

check virtual mechine is alive or not before sending command

qemu/tests/cgroup.py

@@ -1926,7 +1926,9 @@ def run(test, params, env):
         finally:
             error.context("Cleanup")
 
-            session.cmd("true")
+            if vm.is_alive():
+                session.cmd("true")
+
             session.close()
 
             del(cgroup)