Remove image_urls of CirrOS in local.conf.example
Remove image_urls of CirrOS in local.conf.example

CirrOS is default image in latest devstack.
So, The error occurs during run stack.sh like below.

[ERROR] /opt/stack/devstack/stackrc:780
http://download.cirros-cloud.net/0.4.0/cirros-0.4.0-x86_64-disk.img is
duplicate, please remove it from IMAGE_URLS.

Change-Id: Id5a2d06a4c006f042a33fd68fb1b77be7513ee04

openstack/searchlight,openstack/searchlight,openstack/searchlight