[SSSD] [sssd PR#959][opened] tests: fix race confition in enumeration tests

[alexey-tikhonov]

   URL: https://github.com/SSSD/sssd/pull/959
Author: alexey-tikhonov
 Title: #959: tests: fix race confition in enumeration tests
Action: opened

PR body:
"""
This is combination of two patches originally written by @fidencio and @pbrezina.

This PR is a result of extensive discussions held in #947 and #956.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/959/head:pr959
git checkout pr959