[syslinux-iso] Some fixes for automated_script

Fixes FS#23610
Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

configs/syslinux-iso/overlay/etc/rc.d/functions.d/automated_script

 automated_script ()
 {
     script="$(kernel_cmdline script)"
-    if [ -n $script ] ; then
+    if [[ -n "$script" ]]; then
         stat_busy "Configuring $script"
-        if [[ $script =~ ^http:// || $script =~ ^ftp:// ]] ; then
+        if [[ "$script" =~ "^http://" || "$script" =~ "^ftp://" ]]; then
             wget "$script" -q -O /tmp/startup_script >/dev/null
             rt=$?
         else
-            cp $script /tmp/startup_script
+            cp "$script" /tmp/startup_script
             rt=$?
         fi
-        if [ $rt -eq 0 ] ; then
+        if [ $rt -eq 0 ]; then
             chmod +x /tmp/startup_script
-            echo -e "\nif [ \`tty\` = \"/dev/tty1\" ] ; then\n    /tmp/startup_script\nfi\n" >> /root/.bash_profile
+            echo -e '\nif [ $(tty) = "/dev/tty1" ]; then\n    /tmp/startup_script\nfi\n' >> /root/.bash_profile
             stat_done
         else
             stat_fail