Don't leak open fd to virsh in libvirt-guests init script

Running virsh while having /var/lib/libvirt/libvirt-guests file open
makes SELinux emit messages about preventing virsh from reading that
file. Since virsh doesn't really want to read anything, it's better to
run it with /dev/null on stdin to prevent those messages.

daemon/libvirt-guests.init.in

@@ -61,7 +61,7 @@ run_virsh() {
         conn="-c $uri"
     fi
 
-    virsh $conn "$@"
+    virsh $conn "$@" </dev/null
 }
 
 run_virsh_c() {