Remove pointless duplication in setting MOUNT_OPTIONS and DO_MOUNT.
Try to workaround the problem that /etc/krb5.keytab
might have been moved to /etc/krb5.keytab.bu, and
then if mount fails or something, logins to ltsp server
will not work.  ---> change /etc/krb5.keytab handling
to something safer.
rename is_nfs_mounted() to is_mounted() to match
semantics better.
Add imagemagick package as a dependency.

/usr/lib/puavo-ltsp-client/make-release-logo needs "imagemagick".
client: Add ltspguestsshd configuration files for thin client guest session support
client: Actual thin client guest session support. Creates automatically
guest-<hostname> user both on the thin client and on the ltspserver.
(inetd listener is added to TCP 908 on the ltspserver to create the users.)
Lightdm guest account scripts are overwriten on thinclients.

As lightdm's guest session support does not run through PAM stack,
thin client login is done in xsession script. Also normal logins need
to be changed to same model.
client: Fix thinclient guest session cleanup when session finishes.
xexit scripts need LTSP_CLIENT_HOSTNAME set to work properly.
client: Create home directory for thinclient guest users when
logging in through ltspguestsshd and remove the directory if it
already exists.
client: Use device specific language setting from device.json as a fallback
if there's no language set in puavo session.
client: Add a new Xsession.d script that sets PUAVO_SESSION_PATH if it is
not set, but /var/lib/puavo-desktop/users/<user>/puavo_session.json exists.
This is used now for guest sessions that cannot use the PAM scripts to
create the file and set env variables.
client/puavo-thin-guest-account: Create puavo session dir for guest
users and fetch session from puavo-rest automatically.
client: Use the new session starter script for all thin and fat clients.
client: Pass PUAVO_SESSION_ID from thinclient to ltsp server's inetd
listener instead of hostname when initialising the guest user before
ssh login. Still needs work to make user home directory cleaning more
robust.
client: Try harder to find the interface for default route.
client: Fetch device.json also for ltsp servers that need a separate
puavo-rest resource.
client: Use user > session > device fallbacks for locale setting.
client: Temporarily add ltspfs_entry from ltspfsd package so that thin guest
sessions can patch it. Needs to be removed soon.
client: Place ssh socket under /run/puavo/<user>/socket_<server> and
use the path in thin guest sessions for ltspfs mounts. This needs
to be cleaned so that ltspfsd supports ssh sockets running with
user privileges.
client: Place hacked ltspfs_entry file under /lib/udev in puavo-configure-client
on thin clients. This needs to be replaced soon.
client: Modify thin client guest sessions to use lightdm-autologin PAM
stack and existing scripts instead of duplicating code.