Add switch-passwd

Add Source for /sbin/switch-passwd and switch-passwd.service.

The script switch-passwd changes /etc/passwd into a symlink
to passwd.mariux (which is disted) and removes "nis" as
a passwd source from /etc/nsswitch.conf. These changes
are not done, if already done or if gdm is running.

On systems with gdm (workstations) which can't upgrade
immediately, the service switch-passwd.service is used
to do the switch on the next boot.

/etc/passwd and /etc/nsswitch.conf are temporarily disabled
from pdist on the Distmaster to allow a rolling upgrade.

After these files are distributed, all system should execute

    /sbin/switch-passwd    # attempt immediate switch
    systemctl enable switch-passwd.service

After all systems have upgraded (immediate or after reboot) we
can re-enable /etc/passwd and /etc/nsswitch.conf in the Distfile
and remove these switch-passwd files.

install.sh

@@ -88,5 +88,7 @@ install_exec pdist/pdist                          "$DESTDIR$usrlocal_bindir/pdis
 install_exec pmirror/pmirror                      "$DESTDIR$usrlocal_bindir/pmirror"
 install_exec prun/prun                            "$DESTDIR$usr_bindir/prun"
 install_exec put_websafe/put_websafe              "$DESTDIR$usrlocal_bindir/put_websafe"
+install_exec switch-passwd/switch-passwd          "$DESTDIR$root_sbindir/switch-passwd"
+install_data switch-passwd/switch-passwd.service  "$DESTDIR$systemdunitdir/switch-passwd.service"
 
 exit

switch-passwd/switch-passwd

@@ -0,0 +1,11 @@
+#! /bin/sh
+test -L /etc/passwd && exit
+systemctl status gdm.service >/dev/null && exit
+
+set -e
+
+sed -e 's/passwd:     files students nis/passwd:     files students/' < /etc/nsswitch.conf > /etc/nsswitch.conf.new
+ln -sf passwd.mariux /etc/passwd.new
+
+mv /etc/passwd.new /etc/passwd
+mv /etc/nsswitch.conf.new /etc/nsswitch.conf

switch-passwd/switch-passwd.service

@@ -0,0 +1,10 @@
+[Unit]
+Before=gdm.service
+
+[Install]
+WantedBy=basic.target
+
+[Service]
+Type=oneshot
+ExecStart=/sbin/switch-passwd
+RemainAfterExit=true