installation: Fix a bug.

Create EFI/Linux directory if it does not exist.

installation/20install-image.sh

@@ -49,6 +49,7 @@ RELATIVE_EFI_IMAGE_DIR=/EFI/Linux
 if [ ! -f "$image_hash" ]; then
 	wget "$shacache_url/$image_hash"
 fi
+mkdir -p /boot/efi/"$RELATIVE_EFI_IMAGE_DIR"
 cp "$image_hash" /boot/efi/"$RELATIVE_EFI_IMAGE_DIR"
 
 # Delete $default_bootnum so that there is only one boot option for an image created by this script