Title: #880: ci: backport python compatibility patches to 1.16
I did not include Lukas' patche for `test_pam_responder.py` since the affected tests
are not present in 1.16. There was small conflict in `BUILD: Change value of variable
HAVE_PYTHON2/3_BINDINGS` but it was easy to solve. Beside this, there were no conflicts
and the patches has been just cherry-picked.
See the full comment at https://github.com/SSSD/sssd/pull/880#issuecomment-529450477