make internal storage service into init container

[hzy46]

Currently internal storage is used as a service in OpenPAI. We can make it an init container. Using init container has the following advantages:

• Different services can leverage the same logic.
• It is more convenient to ensure the correct storage is mounted.
• Cleaner than current implementation.

Considering there's only one service using internal storage now, it may be not worth the effort to implement the above mechanism. We can leave it to a future work.