Prepend '/' to the delete url for the v2 client

... and update tests to match.

The missing slash results in a non-absolute DELETE request
being sent to the API.
E.g.
DELETE v2/images/62fac489-23b4-4929-87af-2e7236e8542b HTTP/1.1

This is not strictly valid http/1.1 - rfc2616 specifies that the path must
be absolute.
This doesn't cause a problem for the API server, but this can cause
problems if the API server is fronted by something else (see #133161).

It also means that the curl command logged in debug mode has a
bad url.
E.g.
curl -i -X DELETE ... http://10.0.0.13:9292v2/images/...

Change-Id: Ib0c749dedbfcf07303fcddae4512db61b0f3fd78
Closes-bug: #1327101

glanceclient/v2/images.py

@@ -117,7 +117,7 @@ def upload(self, image_id, image_data, image_size=None):
 
     def delete(self, image_id):
         """Delete an image."""
-        self.http_client.json_request('DELETE', 'v2/images/%s' % image_id)
+        self.http_client.json_request('DELETE', '/v2/images/%s' % image_id)
 
     def create(self, **kwargs):
         """Create an image."""

tests/v2/test_images.py

@@ -118,7 +118,7 @@
             },
         ),
     },
-    'v2/images/87b634c1-f893-33c9-28a9-e5673c99239a': {
+    '/v2/images/87b634c1-f893-33c9-28a9-e5673c99239a': {
         'DELETE': (
             {},
             {
@@ -496,7 +496,7 @@ def test_delete_image(self):
         self.controller.delete('87b634c1-f893-33c9-28a9-e5673c99239a')
         expect = [
             ('DELETE',
-                'v2/images/87b634c1-f893-33c9-28a9-e5673c99239a',
+                '/v2/images/87b634c1-f893-33c9-28a9-e5673c99239a',
                 {},
                 None)]
         self.assertEqual(expect, self.api.calls)