The previous patch was wrong for two reasons:
- you can't put shell commands in a Exec, as there's no shell involved
- while you could split the two on two different Exec, it would not
  work anyhow because the unit runs as the esamesync user, and it cannot
  create the /opt/esame directory if the admin did not create it beforehand.

This one was tested to work; the machine boots correctly.

Not tested with labmanager; it is not supposed to be working properly
until you have working copy in /opt/esame, but it would be interesting
to see how it fails.

Otherwise the service will loop and a freshly installed machine
(or a machine with an empty /opt) will not finish the boot.

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