We extend the scripts sage-get-system-packages and sage-print-system-package-command:

• When system=auto, they now invoke sage-guess-package-system.

• sage-print-system-package-command gets a new option --spkg; then it invokes sage-get-system-packages.

This simplifies some uses.

CC: @dimpase

Component: scripts

Author: Matthias Koeppe

Branch/Commit: d75da7e

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/33873