Launch ReadOnlyBootPrompt if $freshInstallIndicator exists.

That file will exist on every read-only media, first boot of writable images
(usb,vmdk), and (if installing directly to partition via the build system or a
mounted image file) hard disk.

The last scenario (of installing directly to hard disk through the build system
or mounted image file) may not be ideal, but it generally tends to be an
advanced installation method. Additionally, it will occur only on first boot.

Fixes #8945.

data/system/boot/Bootscript

@@ -117,7 +117,8 @@ if [ "$SAFEMODE" != "yes" ]; then
 fi
 
 # Now ask the user if he wants to run the Installer or continue to the Desktop.
-if [ "$isReadOnly" = "yes" ]; then
+freshInstallIndicator=/boot/common/settings/fresh_install
+if [ "$isReadOnly" = "yes" -o -e $freshInstallIndicator ]; then
 	# Create Installer link (using the write overlay)
 	ln -sf /boot/system/apps/Installer /boot/home/Desktop/Installer
 
@@ -190,7 +191,6 @@ fi
 
 # Check for fresh install and run post install scripts.
 postInstallDir=/boot/common/boot/post_install
-freshInstallIndicator=/boot/common/settings/fresh_install
 if [ -e $freshInstallIndicator ]; then
 	# wait a moment for things to calm down a bit
 	sleep 3