deflogin: add options '-efu' to shebang of scripts

features.in/deflogin/rootfs/image-scripts.d/50-issue

-#!/bin/sh
+#!/bin/sh -efu
 # issue welcome message if there's a guest user
 # (the first one configured with empty password)
 

features.in/deflogin/rootfs/image-scripts.d/50-root

-#!/bin/sh
+#!/bin/sh -efu
 
 # explicitly requested empty root password
 case "$GLOBAL_ROOTPW_EMPTY" in

features.in/deflogin/rootfs/image-scripts.d/50-users

-#!/bin/sh
+#!/bin/sh -efu
 # add regular user(s) assigning passwords and attributes of power
 
 # NB: care that the utilities exist; shadow-utils is warranted

features.in/deflogin/rootfs/image-scripts.d/70-default-session

-#!/bin/sh
-
-
+#!/bin/sh -efu
 
 [ -n "$GLOBAL_USERS" ] || exit 0
 [ -n "$GLOBAL_DEFAULT_SESSION" ] || exit 0