fix cellv2 delete_host

When trying to delete host that can be found in host_mappings
but not in compute_nodes, current cellv2 delete_host will throw
an exception but does not really handle it.

This patch tries to handle this exception and allow the delete
operation to continue since it shows the host has gone anyway.

Change-Id: I99bd79fb45777edc0e33d846ba478b0a94a1191e
Closes-Bug: #1781391
(cherry picked from commit 0ef4ed96d1)

nova/cmd/manage.py

@@ -1593,7 +1593,10 @@ class CellV2Commands(object):
 
         with context.target_cell(ctxt, cell_mapping) as cctxt:
             instances = objects.InstanceList.get_by_host(cctxt, host)
-            nodes = objects.ComputeNodeList.get_all_by_host(cctxt, host)
+            try:
+                nodes = objects.ComputeNodeList.get_all_by_host(cctxt, host)
+            except exception.ComputeHostNotFound:
+                nodes = []
 
         if instances:
             print(_('There are instances on the host %s.') % host)

nova/tests/unit/test_nova_manage.py

@@ -2075,7 +2075,7 @@ class CellV2CommandsTestCase(test.NoDBTestCase):
     @mock.patch.object(objects.ComputeNodeList, 'get_all_by_host')
     def test_delete_host_success(self, mock_get_cn, mock_destroy,
                                  mock_get_by_host):
-        """Tests trying to delete a host that has not instances."""
+        """Tests trying to delete a host that has no instances."""
         ctxt = context.get_admin_context()
         # create the cell mapping
         cm1 = objects.CellMapping(
@@ -2100,6 +2100,38 @@ class CellV2CommandsTestCase(test.NoDBTestCase):
             self.assertEqual(0, node.mapped)
             node.save.assert_called_once_with()
 
+    @mock.patch.object(objects.InstanceList, 'get_by_host',
+                       return_value=[])
+    @mock.patch.object(objects.HostMapping, 'destroy')
+    @mock.patch.object(objects.ComputeNodeList, 'get_all_by_host',
+        side_effect=exception.ComputeHostNotFound(host='fake-host'))
+    def test_delete_host_success_compute_host_not_found(self, mock_get_cn,
+                                                        mock_destroy,
+                                                        mock_get_by_host):
+        """Tests trying to delete a host that has no instances, but cannot
+           be found by ComputeNodeList.get_all_by_host.
+        """
+        ctxt = context.get_admin_context()
+        # create the cell mapping
+        cm1 = objects.CellMapping(
+            context=ctxt, uuid=uuidsentinel.cell1,
+            database_connection='fake:///db', transport_url='fake:///mq')
+        cm1.create()
+        # create a host mapping in the cell
+        hm = objects.HostMapping(
+            context=ctxt, host='fake-host', cell_mapping=cm1)
+        hm.create()
+
+        self.assertEqual(0, self.commands.delete_host(uuidsentinel.cell1,
+                                                      'fake-host'))
+        output = self.output.getvalue().strip()
+        self.assertEqual('', output)
+        mock_get_by_host.assert_called_once_with(
+            test.MatchType(context.RequestContext), 'fake-host')
+        mock_destroy.assert_called_once_with()
+        mock_get_cn.assert_called_once_with(
+            test.MatchType(context.RequestContext), 'fake-host')
+
 
 class TestNovaManageMain(test.NoDBTestCase):
     """Tests the nova-manage:main() setup code."""