client: Modify puavo-ltsp-init-nfs to mount home directories separately
for each user. On LTSP servers NFS mounts are done with nolock and soft
mount options.

If device.json has tag "sambahomes", the home mounts are done with
mount.cifs instead. In this case /home/share is mounted over NFS.

In this version there's no option to do old style /home as one mount
mounts.
client: Fetch device.json also for ltsp servers that need a separate
puavo-rest resource.
client: Setup also XDG_RUNTIME_DIR under /run/user/<uid> for files
that do not need to be persisted across reboots. Keeps user home
directory cleaner.
client: Fix check for sambahomes tag in puavo-ltsp-init-nfs
client: puavo-ltsp-init-nfs now mounts by default /home as one mount
and uses individual user home mounts over CIFS is sambahomes tag
is set.
client: Fetch device.json also for ltsp servers that need a separate
puavo-rest resource.