Fix image service endpoint path

After converging with telemetry and image, the ceilometer meters and
resources for glance do not appear, the logs show that the glance API
URL is incorrect: http://127.0.0.1:9292/v2/v1.

This patch sets the base path to / so ceilometer can talk to glance.

Change-Id: I656e133995b4cbad12540d03c97adf1164b0f4c5
Closes-Bug: #1293688