Fix for git clone issue during kolla image build

When the first build attempt fail for any reason (e.g. short network
outage, proxy outage,...) then the second attempt always fail for
git source type. Git can't clone repository because destination
directory exists and is not empty.

Current fix checks destination directory and if it exists then
it is removed before cloning.

Change-Id: I949140c49a64baea579d61047e3b2f1240da2771
Closes-Bug: #1706369

kolla/image/build.py

@@ -309,6 +309,11 @@ class BuildTask(DockerTask):
         elif source.get('type') == 'git':
             clone_dir = '{}-{}'.format(dest_archive,
                                        source['reference'].replace('/', '-'))
+            if os.path.exists(clone_dir):
+                self.logger.info("Clone dir %s exists. Removing it.",
+                                 clone_dir)
+                shutil.rmtree(clone_dir)
+
             try:
                 self.logger.debug("Cloning from %s", source['source'])
                 git.Git().clone(source['source'], clone_dir)

kolla/tests/test_build.py

@@ -192,6 +192,28 @@ class TasksTest(base.TestCase):
             else:
                 self.assertIsNotNone(get_result)
 
+    @mock.patch('os.path.exists')
+    @mock.patch('os.utime')
+    @mock.patch('shutil.rmtree')
+    def test_process_git_source_existing_dir(self, mock_rmtree, mock_utime,
+                                             mock_path_exists):
+        source = {'source': 'http://fake/source1', 'type': 'git',
+                  'name': 'fake-image1',
+                  'reference': 'fake/reference1'}
+
+        self.image.source = source
+        self.image.path = "fake_image_path"
+        mock_path_exists.return_value = True
+        push_queue = mock.Mock()
+        builder = build.BuildTask(self.conf, self.image, push_queue)
+        get_result = builder.process_source(self.image, self.image.source)
+
+        mock_rmtree.assert_called_with(
+            "fake_image_path/fake-image1-archive-fake-reference1")
+        self.assertEqual(self.image.status, build.STATUS_ERROR)
+        self.assertFalse(builder.success)
+        self.assertIsNone(get_result)
+
     @mock.patch('docker.APIClient')
     def test_followups_docker_image(self, mock_client):
         self.imageChild.source = {