Refactor duplicate storage related code in redfish.py

[dashmage]

There's a lot of duplicate code shared between the get_storage_drive_data and the get_storage_controller_data methods. Refactor the common code into a separate method (eg: _get_storage_resource_data).

One server may have many different system ids each with multiple storage ids and each of those could have many storage controllers/ storage drives. So we need to think about:

• What does each of these methods (_get_storage_resource_data, get_storage_drive_data/get_storage_controller_data) do?
• What would _get_storage_resource_data return?