Minor edit to the Manage Volumes section of the User Guide

1. Corrected the command to list cinder availability zones
2. Removed the  incorrect output example.

Change-Id: Ie50eacd26fcb5b3370db721ce5fea720bbcbbbb2
backport: none
Closes-Bug: #1377485
Merge "Minor edit to the Manage Volumes section of the User Guide"