sulogin-shell: Use force if SYSTEMD_SULOGIN_FORCE set
    
    When the root account is locked sulogin will either inform you of
    this and not allow you in or if --force is used it will hand
    you passwordless root (if using a recent enough version of util-linux).
    
    Not being allowed a shell is ofcourse inconvenient, but at the same
    time handing out passwordless root unconditionally is probably not
    a good idea everywhere.
    
    This patch thus allows to control which behaviour you want by
    setting the SYSTEMD_SULOGIN_FORCE environment variable to true
    or false to control the behaviour, eg. via adding this to
    'systemctl edit rescue.service' (or emergency.service):
    
    [Service]
    Environment=SYSTEMD_SULOGIN_FORCE=1
    
    Distributions who used locked root accounts and want the passwordless
    behaviour could thus simply drop in the override file in
    /etc/systemd/system/rescue.service.d/override.conf
    
    Fixes: #7115
    Addresses: https://bugs.debian.org/802211
    (cherry picked from commit 33eb44fe4a8d7971b5614bc4c2d90f8d91cce66c)
    
    Resolves: #1625929
    
    patch_name: 0391-sulogin-shell-Use-force-if-SYSTEMD_SULOGIN_FORCE-set.patch
    present_in_specfile: true
    location_in_specfile: 391
    squash_commits: true