Remove 'glance-download' from default import methods

As 'glance-download' requires federated deployments it should
not be enabled by default.

Added line explaining it being available for such deployments
in the config help text.

Change-Id: Icc792e23aad9e7a9a788e6b5826bc5aae54ae978

Author: Erno Kuvaja

glance/common/config.py

@@ -572,11 +572,12 @@
                 item_type=cfg.types.String(quotes=True),
                 bounds=True,
                 default=['glance-direct', 'web-download',
-                         'copy-image', 'glance-download'],
+                         'copy-image'],
                 help=_("""
     List of enabled Image Import Methods
 
     'glance-direct', 'copy-image' and 'web-download' are enabled by default.
+    'glance-download' is available, but requires federated deployments.
 
     Related options:
         * [DEFAULT]/node_staging_uri""")),

glance/tests/unit/v2/test_discovery_image_import.py

@@ -33,12 +33,12 @@ def test_get_import_info_with_empty_method_list(self):
         self.assertEqual([], output['import-methods']['value'])
 
     def test_get_import_info(self):
-        # TODO(rosmaita): change this when import methods are
-        # listed in the config file
-        import_methods = ['glance-direct', 'web-download',
-                          'copy-image', 'glance-download']
+        """Testing defaults, not all possible values"""
+        default_import_methods = ['glance-direct', 'web-download',
+                                  'copy-image']
 
         req = unit_test_utils.get_fake_request()
         output = self.controller.get_image_import(req)
         self.assertIn('import-methods', output)
-        self.assertEqual(import_methods, output['import-methods']['value'])
+        self.assertEqual(default_import_methods,
+                         output['import-methods']['value'])