systemd: reexec systemd to ensure right version is running

SystemD version can differ from initramfs one (which is build in dom0
build environment), so reexec it at startup.

This fixes systemd-212 archlinux issue.

vm-systemd/qubes-sysinit.sh

@@ -14,6 +14,9 @@ read_service() {
     $XS_READ qubes-service/$1 2> /dev/null
 }
 
+# Ensure we're running right version of systemd (the one started by initrd may be different)
+systemctl daemon-reexec
+
 # Wait for evtchn initialization
 while [ ! -e /proc/xen/xenbus ]; do
   sleep 0.1