Included 'cinder extend' command and updated command reference for cinder

Included 'cinder extend' command in the 'Manage Volumes' section of
CLI chapter. Also updated the command reference appendix section
with some new commands.
Partial-Bug: #1239534

Change-Id: Ic546953c3a6202825cbbea247662de6c7451a159
Add Ceilometer install

This adds an initial install of ceilometer to the install guide.

This has not been tested.

Also adds stub sections for adding agents/setting up notification to things.

Change-Id: Ieb154f1412f32279550b0a5a4a0cafc1547b8b61
Merge "Add Ceilometer install"
Merge "Included 'cinder extend' command and updated command reference for cinder"