Generate and source a dib v2 environment

diskimage-builder v2 now relies on the output of "element-info --env
<elements>" to have been sourced into the shell running the element
hooks. Generate the environment and save the output to a file under
environment.d so that dib-run-parts will source it prior to running
hooks.

Change-Id: Ie8ac128e391a7091184b5017959a2a653166062f
Closes-Bug: #1671262

instack/runner.py

@@ -55,6 +55,9 @@ class ElementRunner(object):
         self.no_cleanup = no_cleanup
         self.loaded_elements = {}
         self.tmp_hook_dir = tempfile.mkdtemp()
+        self.environment_file = os.path.join(self.tmp_hook_dir,
+                                             'environment.d',
+                                             '00-dib-v2-env')
 
         # the environment variable should override anything passed in
         if 'ELEMENTS_PATH' in os.environ:
@@ -72,6 +75,14 @@ class ElementRunner(object):
         self.load_dependencies()
         self.process_exclude_elements()
         self.copy_elements()
+        self.generate_environment()
+
+    def generate_environment(self):
+        """Generate a dib v2 environment."""
+        command = ['element-info', '--env'] + list(self.elements)
+        env_output = subprocess.check_output(command)
+        with open(self.environment_file, 'w') as f:
+            f.write(env_output)
 
     def run(self):
         """Apply the elements by running each specified hook."""

instack/tests/test_runner.py

@@ -32,11 +32,18 @@ class TestRunner(testtools.TestCase):
         test_elements = os.path.join(cwd, 'elements')
         self.element_paths = [test_elements]
 
+        self.patcher = mock.patch.object(runner.ElementRunner,
+                                         'generate_environment')
+        self.mock_env = self.patcher.start()
         self.runner = runner.ElementRunner(['dep2', 'echo', 'os'], [],
                                            self.element_paths)
         tmp_dir = tempfile.mkdtemp()
         self.runner.tmp_hook_dir = tmp_dir
 
+    def tearDown(self):
+        super(TestRunner, self).tearDown()
+        self.patcher.stop()
+
     def test_cleanup(self):
         self.runner.cleanup()
         self.assertFalse(os.path.exists(self.runner.tmp_hook_dir))