lang: core: embedded: provisioner: Skip ignore if no drives available

Small bug for certain setups.

lang/core/embedded/provisioner/files/kickstart.ks.tmpl

@@ -84,7 +84,9 @@ usb_disks=$(for dev in /sys/block/sd*; do
 done | paste -sd, -)
 
 # Output the ignoredisk directive to a temporary file.
-echo "ignoredisk --drives=${usb_disks}" > /tmp/ignoredisk.ks
+if [ "${usb_disks}" != "" ]; then
+	echo "ignoredisk --drives=${usb_disks}" > /tmp/ignoredisk.ks
+fi
 %end
 %include /tmp/ignoredisk.ks