Change location of OS-ENDPOINT-POLICY name in API urls.

The current APIs simply put OS-ENDPOINT-POLICY at the start of the
API url. Technically, this should appear in the url at the
location where this differs from the standard core urls.

Partially implements: bp endpoint-policy

Change-Id: I2c49d46e2374aed2411849bd2fd1adf42beaa2c6
Merge "Change location of OS-ENDPOINT-POLICY name in API urls."