[SSSD] [sssd PR#993][synchronized] configure: prefer python3 if available

[arkamar]

   URL: https://github.com/SSSD/sssd/pull/993
Author: arkamar
 Title: #993: configure: prefer python3 if available
Action: synchronized

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/993/head:pr993
git checkout pr993