Add support for image size in v2 api upload

Some backend stores e.g. RBD, will fail if told to create an
image without a valid size (RBD will fail to write to a zero-size
image). Here we add support to allow the image size to be provided
when doing an upload. The result is that the upload content-length
will be set if available either from checking the supplied file
object or as provided by user.

Closes-Bug: 1220197
Change-Id: Ia1f2ea5680a139750d931591949b3e0058148b4b

tests/v2/test_shell_v2.py

@@ -221,13 +221,13 @@ class ShellV2Test(testtools.TestCase):
             self.gc.schemas.get.assert_called_once_with('test')
 
     def test_image_upload(self):
-        args = self._make_args({'id': 'IMG-01', 'file': 'test'})
+        args = self._make_args({'id': 'IMG-01', 'file': 'test', 'size': 1024})
 
         with mock.patch.object(self.gc.images, 'upload') as mocked_upload:
             utils.get_data_file = mock.Mock(return_value='testfile')
             mocked_upload.return_value = None
             test_shell.do_image_upload(self.gc, args)
-            mocked_upload.assert_called_once_with('IMG-01', 'testfile')
+            mocked_upload.assert_called_once_with('IMG-01', 'testfile', 1024)
 
     def test_image_download(self):
         args = self._make_args(