Comment 7 for bug 1756823

Reviewed: https://review.openstack.org/648093
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=7931f85fe66d4e024d7dd5396dcf38378af85470
Submitter: Zuul
Branch: master

commit 7931f85fe66d4e024d7dd5396dcf38378af85470
Author: Silvan Kaiser <email address hidden>
Date: Wed Mar 27 11:47:09 2019 +0100

    Adds systemd detection result caching in Quobyte driver

    Instead of rechecking for systemd multiple times check only
    once and cache the result in the Quobyte driver.

    Furthermore this fixes a range of minor nits like adding
    comments, generalizing the libvirt privsep umount and
    clarifying variable names in related tests, as noted
    in previous change I53f3a062ce419d1142d7dd3103fab565bb105e05 .

    Last but not least this adds unit tests for newly added
    functions in privsep.libvirt, using a fixture from
    change I53b8cca99729bcae6246c79f342f87f55a4ea95c .

    Related-bug: #1756823

    Change-Id: Iba30c49f108af9055de1b1a5c7b1a8406d66cf1a