Reflects Fuel CLI changes about username and pass

The following changes are made into User Guide on Fuel CLI:

* name command (--os-username->--username)
* password command (--os-password-> --password)

Change-Id: I0046c3aeb079397f98c30e94fde9acfac2e2d82f
Closes-Bug: 1384086
Merge "Reflects Fuel CLI changes about username and pass"