migration: reorder code to make it symmetric

In qemu_savevm_state_complete_precopy(), it iterates on each device to add
a json object and transfer related status to destination, while the order
of the last two steps could be refined.

Current order:

    json_start_object()
    	save_section_header()
    	vmstate_save()
    json_end_object()
    	save_section_footer()

After the change:

    json_start_object()
    	save_section_header()
    	vmstate_save()
    	save_section_footer()
    json_end_object()

This patch reorder the code to to make it symmetric. No functional change.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Reviewed-by: NAmit Shah <amit.shah@redhat.com>
Message-Id: <1454626230-16334-1-git-send-email-richard.weiyang@gmail.com>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>

migration/savevm.c

@@ -1088,12 +1088,11 @@ void qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only)
         json_prop_int(vmdesc, "instance_id", se->instance_id);
 
         save_section_header(f, se, QEMU_VM_SECTION_FULL);
-
         vmstate_save(f, se, vmdesc);
-
-        json_end_object(vmdesc);
         trace_savevm_section_end(se->idstr, se->section_id, 0);
         save_section_footer(f, se);
+
+        json_end_object(vmdesc);
     }
 
     if (!in_postcopy) {