keygen.py now recommends that you run it as the user you want to have
ownership of secret.key and uploadkeys (such as www-data for nginx).
Then, if uploadkeys or secret.key don't exist, they will be created with
the correct ownership.
Since keygen.py is run as root, uploadkeys is owned by root. This causes
issues when imgupload.py tries to chmod the uploadkeys file since it
doesn't have permissions to chmod it.
Solution: remove UPLOADKEYS_CHMOD option