Add tests for image model, fix a small bug and remove an unused function

data/model/image.py

@@ -24,7 +24,7 @@ def get_image_with_storage(docker_image_id, storage_uuid):
   """
   try:
     return (Image
-            .select()
+            .select(Image, ImageStorage)
             .join(ImageStorage)
             .where(Image.docker_image_id == docker_image_id,
                    ImageStorage.uuid == storage_uuid)
@@ -355,25 +355,6 @@ def get_image(repo, docker_image_id):
     return None
 
 
-def get_repo_image_by_storage_checksum(namespace, repository_name, storage_checksum):
-  try:
-    return (Image
-            .select()
-            .join(ImageStorage)
-            .switch(Image)
-            .join(Repository)
-            .join(Namespace, on=(Namespace.id == Repository.namespace_user))
-            .where(Repository.name == repository_name, Namespace.username == namespace,
-                   ImageStorage.content_checksum == storage_checksum,
-                   ImageStorage.uploading == False)
-            .get())
-  except Image.DoesNotExist:
-    msg = 'Image with storage checksum {0} does not exist in repo {1}/{2}'.format(storage_checksum,
-                                                                                  namespace,
-                                                                                  repository_name)
-    raise InvalidImageException(msg)
-
-
 def synthesize_v1_image(repo, image_storage_id, storage_image_size, docker_image_id,
                         created_date_str, comment, command, v1_json_metadata, parent_image=None):
   """ Find an existing image with this docker image id, and if none exists, write one with the