Cifs Unmount

To unmount the cifs shared drives before shutdown the following service-script must be edited:
/lib/systemd/system/wpa_supplicant.service ( as described in https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1431774)

[Unit]
Description=WPA supplicant
Before=network.target

[Service]
Type=dbus
BusName=fi.epitest.hostap.WPASupplicant
ExecStart=/sbin/wpa_supplicant -u -s -O /run/wpa_supplicant

[Install]
WantedBy=multi-user.target
Alias=dbus-fi.epitest.hostap.WPASupplicant.service

This works !