Different exit code in new versions of iscsiadm

Fixes bug #932356
For "iscsiadm: No records found"
if version <= 2.0-871 iscsiadm returns 255
newer versions return 21

Change-Id: Ib4319ed11b20a339b439c70574d0d45acc8814fa

nova/virt/libvirt/volume.py

@@ -114,7 +114,8 @@ def connect_volume(self, connection_info, mount_device):
         try:
             self._run_iscsiadm(iscsi_properties, ())
         except exception.ProcessExecutionError as exc:
-            if exc.exit_code == 255:
+            # iscsiadm returns 21 for "No records found" after version 2.0-871
+            if exc.exit_code in [21, 255]:
                 self._run_iscsiadm(iscsi_properties, ('--op', 'new'))
             else:
                 raise