They could contain local modification made by the admin,
so we will just create them when they are not present,
and leave them as they are if they are already on the machine.

It is optional, but it is easier if it's already there, ready to be
modified.

Added a new multi-user target for targets esame*, so we can avoid to start NFS services if not needed

The first commit (the one that was reverted) contained a spurious,
unrelated change.

This reverts commit 2ed8cbd1.

The bta-no-usbpen was a link to /bin/sleep.

Passaggio ai target secondari (esame e graphical) attraverso comando 'start' invece di 'isolate' (NetworkManager non ripartiva più dopo il passaggio di target)

Forgot to add esame-get-config.timer to esameshow.target and the target itself in the install script.

New feature (fix for someone...): don't erase user's home if the computer crashes or reboots during the exam.
The user's home is erased (if required) only when the exam mode starts the first time.

Added esamesync-esame.service to graphical.target requirements, so the boot process stops if the master server is not reachable.

Otherwise we would get something like this:

  useradd: user 'rdesktop' already exists
  Error creating user rdesktop
  User rdesktop was created

Removed esame-get-config-boot.service as a requirement from some services (it is not needed anymore as esame-configurator target is reached before any other target at boot time).