Catch iscsi VolumeDeviceNotFound when detaching

If exceptions are raised, nova-compute can't start
when executing _destroy_evacuated_instances.

Change-Id: I0a2877ec0f922d2bc9a742d1c2c2540a6b77e9ce
Closes-Bug: #1532657

nova/tests/unit/virt/libvirt/volume/test_iscsi.py

@@ -11,6 +11,7 @@
 #    under the License.
 
 import mock
+from os_brick import exception as os_brick_exception
 from os_brick.initiator import connector
 
 from nova.tests.unit.virt.libvirt.volume import test_volume
@@ -88,3 +89,18 @@ Setting up iSCSI targets: unused
         self.assertEqual(device_path, tree.find('./source').get('dev'))
         self.assertEqual('raw', tree.find('./driver').get('type'))
         self.assertEqual('native', tree.find('./driver').get('io'))
+
+    @mock.patch.object(iscsi.LOG, 'warning')
+    def test_libvirt_iscsi_driver_disconnect_volume_with_devicenotfound(self,
+            mock_LOG_warning):
+        device_path = '/dev/fake-dev'
+        connection_info = {'data': {'device_path': device_path}}
+
+        libvirt_driver = iscsi.LibvirtISCSIVolumeDriver(self.fake_conn)
+        libvirt_driver.connector.disconnect_volume = mock.MagicMock(
+            side_effect=os_brick_exception.VolumeDeviceNotFound(
+                device=device_path))
+        libvirt_driver.disconnect_volume(connection_info, device_path)
+
+        msg = mock_LOG_warning.call_args_list[0]
+        self.assertIn('Ignoring VolumeDeviceNotFound', msg[0][0])

nova/virt/libvirt/volume/iscsi.py

@@ -11,10 +11,12 @@
 #    under the License.
 """Libvirt volume driver for iSCSI"""
 
+from os_brick import exception as os_brick_exception
 from os_brick.initiator import connector
 from oslo_config import cfg
 from oslo_log import log as logging
 
+from nova.i18n import _LW
 from nova import utils
 from nova.virt.libvirt.volume import volume as libvirt_volume
 
@@ -91,7 +93,11 @@ class LibvirtISCSIVolumeDriver(libvirt_volume.LibvirtBaseVolumeDriver):
         """Detach the volume from instance_name."""
 
         LOG.debug("calling os-brick to detach iSCSI Volume")
-        self.connector.disconnect_volume(connection_info['data'], None)
+        try:
+            self.connector.disconnect_volume(connection_info['data'], None)
+        except os_brick_exception.VolumeDeviceNotFound as exc:
+            LOG.warning(_LW('Ignoring VolumeDeviceNotFound: %s'), exc)
+            return
         LOG.debug("Disconnected iSCSI Volume %s", disk_dev)
 
         super(LibvirtISCSIVolumeDriver,