glance storage rbd parameters are enabled.

Closes-Bug: #1379467
Issue: In icehouse, glance-api.conf  configs
       "rbd_store_chunk", "rbd_store_pool" and
       "rbd_store_ceph_conf" configs are disabled by
       default. storage rbd parameters are disabled by default
Fix: enabled the above mentioned storage rbd parameters.
Test: validated with "fab setup_storage" run

Change-Id: I2a1c38ce8e329d24e9c6e8f3aef67f5cda435f7d