CRUD on flavor extra spec extension should be admin-only

Changes the default policy.json file to make the flavor extra
spec create/update/delete operations admin-only, since the
flavormanage extension is admin-only.

fixes: lp bug #1094142

Change-Id: Ic464b17130e76565a7c475e59064e3e3e8861327
Merge "CRUD on flavor extra spec extension should be admin-only"