dom0: use /bin/bash as interpreter of qubes_prepare_saved_domain.sh

Required for ex $(( )) construction. /bin/sh may not handle it (when linked to
some other shell than bash).

dom0/restore/qubes_prepare_saved_domain.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 get_encoded_script()
 {
 	if ! [ -f "$1" ] ; then