allow power-on to fail on finish_resize

Power-on is the very last step of a resize/migration.
Failing at this point would leave a VM in a quite inconsistent
state in the DB and in the vCenter.
In case power-on fails, we log an error and let nova continue
putting the vm into VERIFY_RESIZE state. One can then manually
attempt to power-on the VM or revert the resize.

Change-Id: Ic979ce5d7eaf478e5130182a656996cc5f1af29a

nova/tests/unit/virt/vmwareapi/test_vmops.py

@@ -675,7 +675,8 @@ def test_clean_shutdown_no_vwaretools(self):
 
     def _test_finish_migration(self, power_on=True,
                                resize_instance=False, migration=None,
-                               no_nics=False, is_bigvm=False):
+                               no_nics=False, is_bigvm=False,
+                               power_on_err=None):
         with test.nested(
                 mock.patch.object(self._vmops,
                                   '_resize_create_ephemerals_and_swap'),
@@ -741,6 +742,9 @@ def _test_finish_migration(self, power_on=True,
                 self._instance.memory_mb = 2048 * 1024  # 2 TiB RAM
                 self._instance.flavor.memory_mb = 2048 * 1024  # 2 TiB RAM
 
+            if power_on_err:
+                fake_power_on.side_effect = power_on_err
+
             self._vmops.finish_migration(context=self._context,
                                          migration=migration,
                                          instance=self._instance,
@@ -809,6 +813,12 @@ def _test_finish_migration(self, power_on=True,
     def test_finish_migration_power_on(self):
         self._test_finish_migration(power_on=True, resize_instance=False)
 
+    @mock.patch.object(vmops.LOG, 'exception')
+    def test_finish_migration_power_on_fails(self, log_mock):
+        power_on_err = vexc.VimException()
+        self._test_finish_migration(power_on=True, power_on_err=power_on_err)
+        log_mock.assert_called_once_with(mock.ANY, instance=self._instance)
+
     def test_finish_migration_power_off(self):
         self._test_finish_migration(power_on=False, resize_instance=False)
 

nova/virt/vmwareapi/vmops.py

@@ -2730,7 +2730,11 @@ def finish_migration(self, context, migration, instance, disk_info,
                                        total_steps=RESIZE_TOTAL_STEPS)
 
         if power_on:
-            vm_util.power_on_instance(self._session, instance)
+            try:
+                vm_util.power_on_instance(self._session, instance)
+            except vexc.VimException:
+                LOG.exception("Failed to power on the VM.",
+                              instance=instance)
 
     def _get_vm_networking_spec(self, instance, network_info):
         client_factory = self._session.vim.client.factory