kernel-install: Reuse $BOOT/Default if it already exists

Avoids duplicate installation problems when the machine ID is
initialized after a kernel is already installed under $BOOT/Default.

src/kernel-install/kernel-install

@@ -85,7 +85,10 @@ fi
 KERNEL_VERSION="$1"
 KERNEL_IMAGE="$2"
 
-if [[ -f /etc/machine-id ]]; then
+# Reuse directory created without a machine ID present if it exists.
+if [[ -d /efi/Default ]] || [[ -d /boot/Default ]] || [[ -d /boot/efi/Default ]]; then
+    MACHINE_ID="Default"
+elif [[ -f /etc/machine-id ]]; then
     read MACHINE_ID < /etc/machine-id
 else
     MACHINE_ID="Default"