Make LXC fail verification if cgroup is not mounted

Since LXC now relies on cgroup memory limits to enforce memory, let's
make hypervisor verification (and thus cluster-verify) return errors
when the cgroup filesystem is not mounted.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>

lib/hypervisor/hv_lxc.py

 #
 #
 
-# Copyright (C) 2010 Google Inc.
+# Copyright (C) 2010, 2013 Google Inc.
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -425,10 +425,18 @@ class LXCHypervisor(hv_base.BaseHypervisor):
     @return: Problem description if something is wrong, C{None} otherwise
 
     """
-    if os.path.exists(self._ROOT_DIR):
-      return None
-    else:
-      return "The required directory '%s' does not exist" % self._ROOT_DIR
+    msgs = []
+
+    if not os.path.exists(self._ROOT_DIR):
+      msgs.append("The required directory '%s' does not exist" %
+                  self._ROOT_DIR)
+
+    try:
+      self._GetCgroupMountPoint()
+    except errors.HypervisorError, err:
+      msgs.append(str(err))
+
+    return self._FormatVerifyResults(msgs)
 
   @classmethod
   def PowercycleNode(cls):