get-config: when there is no configuration, wait and retry later.

This will help troubleshooting, as the future sysadmins will connect to
the machine, run `journalctl -f ` to see what's wrong with the machine,
and in about 30 seconds they will see:

  Error fetching machine configuration!
  Error fetching machine info!
  If this is a new machine, did you add it into labmanager-admin?

So they will know what's wrong, and how to correct it.

bin/get-config

@@ -166,10 +166,12 @@ updateCurrentConfigId() {
 
 function getConfig() {
     getConfigVars
-    if [[ $? != 0 ]]; then
-        debug "Error fetching machine info!"
-        return 1
-    fi
+    while [[ $? != 0 ]]; do
+        echo "Error fetching machine info!"
+        echo "If this is a new machine, did you add it into labmanager-admin?"
+        sleep 30;
+        getConfigVars
+    done
 
     # back config files up
     cp -f /local/esame-machine.conf /local/esame-machine.conf.prev >/dev/null 2>&1