boottest - Add exception handling for manifest fetching

boottest.py

@@ -79,7 +79,13 @@ class TouchManifest(object):
                 "I: [%s] - Fetching manifest from %s" % (
                     time.asctime(), url))
             print("I: [%s] - saving it to %s" % (time.asctime(), self.path))
-        response = urllib.urlopen(url)
+        try:
+            response = urllib.urlopen(url)
+        except IOError as e:
+            print("W: [%s] - error connecting to %s" % (
+                    time.asctime(), self.path))
+            return success  # failure
+
         # Only [re]create the manifest file if one was successfully downloaded
         # this allows for an existing image to be used if the download fails.
         if response.code == 200:

tests/test_boottest.py

@@ -89,6 +89,14 @@ class TestTouchManifest(unittest.TestCase):
         self.assertEqual(1, len(manifest._manifest))
         self.assertIn('foo', manifest)
 
+    def test_fetch_excpetion(self):
+        _p = mock.patch('urllib.urlopen')
+        mocked_urlopen = _p.start()
+        self.addCleanup(_p.stop)
+        mocked_urlopen.side_effect = [IOError("connection refused")]
+        manifest = boottest.TouchManifest('not-real', 'not-real')
+        self.assertEqual(0, len(manifest._manifest))
+
     def test_simple(self):
         # Existing manifest file allows callsites to properly check presence.
         manifest_dir = os.path.join(self.imagesdir, 'ubuntu/vivid')