esamesync-esame: do not run if /opt/esame was not created.

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.

systemd-ubuntu/esamesync-esame.service

@@ -3,6 +3,10 @@ Description=esamesync esame
 After=network-online.target
 Wants=network-online.target
 Before=display-manager.service getty.target
+# Do not run if /opt/esame was not created.
+# We do not check the permissions, but it must be writable by
+# the esamesync user/group.
+ConditionPathIsDirectory=/opt/esame
 
 [Service]
 Environment=RUNLEVEL=3
@@ -10,7 +14,6 @@ Environment=RUNLEVEL=3
 #ExecStart=/etc/init.d/esamesync esame
 User=esamesync
 Group=esamesync
-ExecStartPre=-mkdir -p /opt/esame && chown esamesync:esamesync /opt/esame
 ExecStart=/usr/libexec/labmanager/esamesync-esame.sh
 #TimeoutSec=0
 RemainAfterExit=yes