[SSSD] [sssd PR#809][opened] sss_cache: Do nothing if SYSTEMD_OFFLINE=1

[thalman]

   URL: https://github.com/SSSD/sssd/pull/809
Author: thalman
 Title: #809: sss_cache: Do nothing if SYSTEMD_OFFLINE=1
Action: opened

PR body:
"""
Running `rpm-ostree compose tree` results in a big spam. This is because rpm-ostree
doesn't want scripts writing into `/var`; it's system-administrator managed
state.

Let's just silently do nothing if we're running offline, as there won't be a
sssd running.

The original suggestion can be found here:
https://pagure.io/SSSD/sssd/pull-request/3959

"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/809/head:pr809
git checkout pr809