Fix v2.1 API os-simple-tenant-usage policy

Current etc/policy.json contains typos about os-simple-tenant-usage of
v2.1 API and the authorization doesn't work at all.
This patch fixes the typos.

Partially implements blueprint v2-on-v3-api

Change-Id: I2d1c3290fe336219fcc5523d26b1f8c11e35566f
Merge "Fix v2.1 API os-simple-tenant-usage policy"