More changes for registry-v2 in python.

Implement the minimal changes to the local filesystem storage driver and feed them through the distributed storage driver.
Create a digest package which contains digest_tools and checksums.
Fix the tests to use the new v1 endpoint locations.
Fix repository.delete_instance to properly filter the generated queries to avoid most subquery deletes, but still generate them when not explicitly filtered.

auth/jwt_auth.py

@@ -61,7 +61,7 @@ def process_jwt_auth(func):
         return (None, 'Invalid username or password')
 
       username = payload['sub']
-      loaded_identity = Identity(username, 'signed_grant')
+      loaded_identity = Identity(username, 'signed_jwt')
 
       # Process the grants from the payload
       if 'access' in payload: