Cleanup: remove unused code from store_utils

store_utils.py contains several methods not used anywhere in the
codebase.
This patch removes the unused code.

Change-Id: I8faa87e1dcce053b19a37c19856eb53529e0ec78
Closes-Bug: #1262051
Fixed wrong string format in glance.api.v2.image_data

Closes bug 1264089

Change-Id: If6d72406b0e717f0f944a0b9d1ab4a0fc9301e6a
Merge "Fixed wrong string format in glance.api.v2.image_data"
Merge "Cleanup: remove unused code from store_utils"