how to sand-plaster a plaster wall without spreading plaster dust everywhere?
You can use a Drywall Vacuum sander http://amzn.to/2uWPcdB that connects to a vacuum. The vacuum will pick up the vast majority of dust that gets created. 

These things use a special abrasive screen/sandpaper that allows the dust being created to pass through the screen/sandpaper and into your vacuum cleaner. This also helps prevent the abrasives from clogging due to dust.