install-labmanager: fix a small typo in the comparison.

install-labmanager.sh

@@ -38,7 +38,7 @@ OLD_FILES=(
 
 # Create a users
 myuseradd() {
-  if [ "z$1" != "z" ]; then
+  if [ "z$1" == "z" ]; then
     echo "myuseradd: No user specified! Nothing to do."
     return
   fi