Update list_instances to catch libvirtError.

Commit be590cfa4b caught (and tested
for) the wrong exception. lookupByID throws a libvirtError.

Fixes LP Bug #1032741.

Change-Id: I6745660658df4d0f2bc4cd423e173200fc23cd8e

nova/tests/test_libvirt.py

@@ -912,10 +912,10 @@ class LibvirtConnTestCase(test.TestCase):
         # Only one should be listed, since domain with ID 0 must be skiped
         self.assertEquals(len(instances), 1)
 
-    def test_list_instances_when_not_found(self):
+    def test_list_instances_when_instance_deleted(self):
 
         def fake_lookup(instance_name):
-            raise exception.InstanceNotFound()
+            raise libvirt.libvirtError("we deleted an instance!")
 
         self.mox.StubOutWithMock(libvirt_driver.LibvirtDriver, '_conn')
         libvirt_driver.LibvirtDriver._conn.lookupByID = fake_lookup

nova/virt/libvirt/driver.py

@@ -417,7 +417,7 @@ class LibvirtDriver(driver.ComputeDriver):
                 if domain_id != 0:
                     domain = self._conn.lookupByID(domain_id)
                     names.append(domain.name())
-            except exception.InstanceNotFound:
+            except libvirt.libvirtError:
                 # Instance was deleted while listing... ignore it
                 pass
         return names