Install Guide: Edits for section_cinder-controller.xml

This is a forward port of editorial changes done to
https://review.openstack.org/#/c/62667.

Change-Id: Ia5dac71e761d1f423ad75db70e599ad08ad0a8d0
backport: none (already in havana)
Merge "Install Guide: Edits for section_cinder-controller.xml"