Optimize systemd dependency for containers

According to https://fedoraproject.org/wiki/Packaging:Scriptlets:
If a package is suitable for installation without systemd (in a
container image, for example) and does not require any of the
systemd mechanisms such as tmpfiles.d, then the systemd_ordering macro
MAY be used instead of the systemd_requires macro.

That is exactly the case we want to address for container images
when installing packages in it.

Resolves: rhbz#1668688
Related-Bug: #1804822
Signed-off-by: Bogdan Dobrelya <bdobreli@redhat.com>

rsyslog.spec

@@ -9,7 +9,7 @@
 Summary: Enhanced system logging and kernel message trapping daemon
 Name: rsyslog
 Version: 8.39.0
-Release: 1%{?dist}
+Release: 2%{?dist}
 License: (GPLv3+ and ASL 2.0)
 Group: System Environment/Daemons
 URL: http://www.rsyslog.com/
@@ -39,9 +39,7 @@ BuildRequires: qpid-proton-c-devel
 
 Requires: logrotate >= 3.5.2
 Requires: bash >= 2.0
-Requires(post): systemd
-Requires(preun): systemd
-Requires(postun): systemd
+%{?systemd_ordering}
 
 Provides: syslog
 Obsoletes: sysklogd < 1.5-11
@@ -503,6 +501,9 @@ done
 %doc %{rsyslog_docdir}/k8s_container_name.rulebase
 
 %changelog
+* Wed Jan 23 2019 Bogdan Dobrelya <bdobreli@redhat.com> - 8.39.0-2
+- Use systemd_ordering macro
+
 * Wed Dec 05 2018 Jiri Vymazal <jvymazal@redhat.com> - 8.39.0-1
 - rebase to upstream version 8.39.0
   resolves: rhbz#1649081