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

[arkamar]

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

PR body:
"""
We should prefer python3 every time when it is available regardless of
whether python3 binding are generated, otherwise `sbus_generate.sh` fails
in python3 only systems, where sssd is configured with
`--without-python3-bindings` parameter.
"""

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