Bugfix storage block get fails to provide data

- Fixes bug that was causing data not to be returned when retrieving a block through the storage block get end-point
  - block model needed to have the storage id told to it since there was no metadata storage id
  - adds a specific test for this scenario to the unit testing
- improves clarity in the storage drivers between block_id usages
Don't know why we had this; it's identical to the one in the interface class; all unit tests pass fine with it removed.

Probably left over from an older re-factor