Update [glance] section in nova.conf for Juno

Use new parameters for Juno like it's documented here:
http://docs.openstack.org/trunk/config-reference/content/nova-conf-changes-master.html
* Use [glance] section
* Delete the glance_ prefix when needed

Closes-bug #1391099

Change-Id: Id6619de87e27b5b476a3bf78387db6c1f52ea4ac
Merge "Update [glance] section in nova.conf for Juno"