Fix Cell description

Issues fixed:
* Remove obsolete comment about cell scheduling
* Fix api username/password to follow previous example
* Add missing closing parenthesis
* Wrap overlong screen lines
* Use replaceable for example

Change-Id: If99ec8d091ee1f7abfb4138e0668e0de9c3a97cf
Closes-Bug: #1315136
Fixing deprecated libvirt options for nova.conf

[DEFAULT] => [libvirt]
libvirt_type => virt_type
libvirt_NAME => NAME

Closes-bug: #1253812

Change-Id: I154ff62954bda5562f7e9c9ca1e56feecf18faf1
Merge "Fixing deprecated libvirt options for nova.conf"
Merge "Fix Cell description"