Add an optional parameter --append

This patch will add an optional parameter --append to the glanceclient
command md-tag-create-multiple to provide the facility of appending
the tags.
If the parameter is present  it will append the tags to existing one,
else it will overwrite the existing tags.

Depends-On: https://review.opendev.org/c/openstack/glance/+/804966
Change-Id: I1841e7146da76b13f4cd8925e19f59d0eaf08f7a

glanceclient/tests/unit/v2/test_shell_v2.py

@@ -3084,7 +3084,8 @@ class ShellV2Test(testtools.TestCase):
     def test_do_md_tag_create_multiple(self):
         args = self._make_args({'namespace': 'MyNamespace',
                                 'delim': ',',
-                                'names': 'MyTag1, MyTag2'})
+                                'names': 'MyTag1, MyTag2',
+                                'append': False})
         with mock.patch.object(
                 self.gc.metadefs_tag, 'create_multiple') as mocked_create_tags:
             expect_tags = [{'tags': [{'name': 'MyTag1'}, {'name': 'MyTag2'}]}]
@@ -3094,7 +3095,28 @@ class ShellV2Test(testtools.TestCase):
             test_shell.do_md_tag_create_multiple(self.gc, args)
 
             mocked_create_tags.assert_called_once_with(
-                'MyNamespace', tags=['MyTag1', 'MyTag2'])
+                'MyNamespace', tags=['MyTag1', 'MyTag2'], append=False)
+            utils.print_list.assert_called_once_with(
+                expect_tags,
+                ['name'],
+                field_settings={
+                    'description': {'align': 'l', 'max_width': 50}})
+
+    def test_do_md_tag_create_multiple_with_append(self):
+        args = self._make_args({'namespace': 'MyNamespace',
+                                'delim': ',',
+                                'names': 'MyTag1, MyTag2',
+                                'append': True})
+        with mock.patch.object(
+                self.gc.metadefs_tag, 'create_multiple') as mocked_create_tags:
+            expect_tags = [{'tags': [{'name': 'MyTag1'}, {'name': 'MyTag2'}]}]
+
+            mocked_create_tags.return_value = expect_tags
+
+            test_shell.do_md_tag_create_multiple(self.gc, args)
+
+            mocked_create_tags.assert_called_once_with(
+                'MyNamespace', tags=['MyTag1', 'MyTag2'], append=True)
             utils.print_list.assert_called_once_with(
                 expect_tags,
                 ['name'],