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.
Merge branch 'master' into home-mounts
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.
clients: Add support for home directories over CIFS in puavo-ltsp-init-nfs.
This can be activated by tag sambahomes in device settings. Device tags
were added in puavo-rest commit a396a9ac31341cfad5bda429b636dfd4d894be2b.

The new functionality is added to test whether CIFS would work better for
user homes than NFS.