Add module 'write-files-deferred' executed in stage 'final' (#916)

The main idea is to introduce a second module that takes care of
writing files, but in the 'final' stage.

While the introduction of a second module would allow for choosing
the appropriate place withing the order of modules (and stages),
there is no addition top-level directive being added to the cloud
configuration schema. Instead, 'write-files' schema is being extended
to include a 'defer' attribute used only by the 'write-deffered-files'
modules.

The new module 'write-deferred-files' reuses as much as
possible of the 'write-files' functionality.

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/unittests/test_handler/test_handler_write_files.py b/tests/unittests/test_handler/test_handler_write_files.py
index 727681d3..0af92805 100644
--- a/tests/unittests/test_handler/test_handler_write_files.py
+++ b/tests/unittests/test_handler/test_handler_write_files.py
@@ -189,6 +189,19 @@ class TestWriteFiles(FilesystemMockingTestCase):
             len(gz_aliases + gz_b64_aliases + b64_aliases) * len(datum))
         self.assertEqual(len(expected), flen_expected)
 
+    def test_deferred(self):
+        self.patchUtils(self.tmp)
+        file_path = '/tmp/deferred.file'
+        config = {
+            'write_files': [
+                {'path': file_path, 'defer': True}
+            ]
+        }
+        cc = self.tmp_cloud('ubuntu')
+        handle('cc_write_file', config, cc, LOG, [])
+        with self.assertRaises(FileNotFoundError):
+            util.load_file(file_path)
+
 
 class TestDecodePerms(CiTestCase):