When deleting an instance, avoid freakout if iscsi device is gone

It's fairly easy to get into a state where an instance is not running,
the iscsi infrastructure has been torn down, and the instance cannot
be deleted because the iscsi device cannot be successfully removed.
This patch ignores the associated return value for that scenario and
marches forward in the teardown process.

Fixes bug 1079745 (Cherry picked for Essex)

Change-Id: Ib28790892eebe341ac10a92250cf872605fefe9b

nova/virt/libvirt/volume.py

@@ -112,10 +112,11 @@ def _run_iscsiadm(self, iscsi_properties, iscsi_command, **kwargs):
                   (iscsi_command, out, err))
         return (out, err)
 
-    def _iscsiadm_update(self, iscsi_properties, property_key, property_value):
+    def _iscsiadm_update(self, iscsi_properties, property_key, property_value,
+                         **kwargs):
         iscsi_command = ('--op', 'update', '-n', property_key,
                          '-v', property_value)
-        return self._run_iscsiadm(iscsi_properties, iscsi_command)
+        return self._run_iscsiadm(iscsi_properties, iscsi_command, **kwargs)
 
     @utils.synchronized('connect_volume')
     def connect_volume(self, connection_info, mount_device):
@@ -201,7 +202,8 @@ def disconnect_volume(self, connection_info, mount_device):
         devices = self.connection.get_all_block_devices()
         devices = [dev for dev in devices if dev.startswith(device_prefix)]
         if not devices:
-            self._iscsiadm_update(iscsi_properties, "node.startup", "manual")
+            self._iscsiadm_update(iscsi_properties, "node.startup", "manual",
+                                  check_exit_code=[0, 255])
             self._run_iscsiadm(iscsi_properties, ("--logout",),
                                check_exit_code=[0, 255])
             self._run_iscsiadm(iscsi_properties, ('--op', 'delete'),