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#1668687
Related-Bug: #1804822

Signed-off-by: Bogdan Dobrelya <bdobreli@redhat.com>

iputils.spec

@@ -3,7 +3,7 @@
 Summary: Network monitoring tools including ping
 Name: iputils
 Version: 20180629
-Release: 2%{?dist}
+Release: 3%{?dist}
 # some parts are under the original BSD (ping.c)
 # some are under GPLv2+ (tracepath.c)
 License: BSD and GPLv2+
@@ -28,10 +28,8 @@ BuildRequires: libidn2-devel
 BuildRequires: openssl-devel
 BuildRequires: libcap-devel
 BuildRequires: libxslt docbook-style-xsl
-Requires(post): systemd
-Requires(preun): systemd
-Requires(postun): systemd
 BuildRequires: systemd
+%{?systemd_ordering}
 Provides: /bin/ping
 Provides: /bin/ping6
 Provides: /sbin/arping
@@ -154,6 +152,9 @@ install -m 644 %SOURCE3 ${RPM_BUILD_ROOT}/%{_unitdir}
 %attr(644,root,root) %{_mandir}/man8/ninfod.8.gz
 
 %changelog
+* Wed Jan 23 2019 Bogdan Dobrelya <bdobreli@redhat.com> - 20180629-3
+- Use systemd_ordering macro
+
 * Fri Jul 13 2018 Fedora Release Engineering <releng@fedoraproject.org> - 20180629-2
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_29_Mass_Rebuild