I’ve recently started to use Illustrator CC 2017 (so far I used CS5).
I noticed that line object doesn’t have a classic “4 node” bounding box as earlier, just “two nodes”. It allows rotation, but not scale of the line. I can grab one anchor and hold ALT so the transformation is around center, but that way I can’t be sure that angle is retained. Earlier I would hold ALT+SHIFT, but now SHIFT just locks 45/90 angle.
If the reason for wanting the handles is so that you can shorten / lengthen straight lines while retaining the original angle then this can be achieved by turning on Smart Guides. Grabbing either end of the line will bring up a smart guide that shows you when you are retaining the angle. It pops up with the ‘Line Extension’ Smart Guide label.
Hope that helps.