Bug # 1197054 - Added new official fedora cloud image link.

Fedora now includes 'official' cloud images, rather than the
unofficial ones provided in earlier releases. As such I have
updated the relevant paragraph to link to these.

Conflicts:
	doc/src/docbkx/openstack-image/ch_obtaining_images.xml

Cherry picked from http://review.openstack.org/35341

Change-Id: Ia5f5ceffb206431262396d58ac1e1f4973c01a68