client: New PAM script setup-guest-session to run guest session
initialisation that needs to be done during PAM login. Now it
only sets env variable "GUEST_SESSION=true" that can be used in
later phases to distinguish between normal and guest sessions.
client: Add custom PAM stack for laptop guest logins.
client: Move PAM scripts from /usr/lib/puavo-ltsp-client/ to
/usr/lib/puavo-ltsp-client/pam/ as the directory contains also
other scripts that are not run from PAM.
client: Start using the custom PAM stack for laptop guest logins.
client: Laptop guest logins need "export HOMEPAGE" for cases when
puavo session is not available and device.json is used to determine
browser homepage.
client: Call setup-guest-session also during guest logins on thin/fat
clients.
Remove pam_gnome_keyring.so from guest logins,
those are not needed there.
Add pam_gnome_keyring.so to ltspsshd so that gnome-keyring
works properly in thin clients.
Do not enable screen locking for guest users

(It makes no sense to lock the screen when there is password
to open it).
Merge remote-tracking branch 'origin/laptop_pam_guest'

Add support for laptop guest logins, and also set GUEST_SESSION
environment varible so that on desktop session different components
can change their behaviour based on that (if necessary).