spec: Only call ldconfig on RHEL7

Since Fedora 28 (our minimum supported build), ldconfig is called
automatically for us:

https://fedoraproject.org/wiki/Changes/Removing_ldconfig_scriptlets

These changes appear to be implemented for RHEL > 7 as well, so only
run ldconfig on RHEL7
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NCole Robinson <crobinso@redhat.com>

libvirt.spec.in

@@ -1480,12 +1480,16 @@ exit 0
 
 %post client
 
+%if 0%{?rhel} == 7
 /sbin/ldconfig
+%endif
 %systemd_post libvirt-guests.service
 
 %postun client
 
+%if 0%{?rhel} == 7
 /sbin/ldconfig
+%endif
 %systemd_postun libvirt-guests.service
 
 %triggerun client -- libvirt < 0.9.4