Some new linux releases don't seem to include a python executable. They have python3 but no python or python2. Sage should build on such systems.

CC: @isuruf @kiwifb @timokau @antonio-rojas

Component: build

Author: John Palmieri

Branch: 7a27daa

Reviewer: Volker Braun

Issue created by migration from https://trac.sagemath.org/ticket/28657