Fix for host env leak into grub

While building images in a dual boot host,
/dev/sda is leaking into build's grub config.
It is visible in the logs that the commands
GRUB-INSTALL and GRUB-MKCONFIG probes Host OS environment.
This is avoided by setting grub_disable_os_prober
to true in /default/grub config file.

Change-Id: I7408de7b3bc8a62f8bf103f00a88a596f988353c
Closes-Bug: 1166491

elements/vm/finalise.d/51-bootloader

@@ -135,8 +135,24 @@ function install_grub2 {
             sed -i -e 's/\(^GRUB_CMDLINE_LINUX.*\)"$/\1 nofb nomodeset vga=normal"/' /etc/default/grub
         ;;
     esac
+
+    # os-prober leaks /dev/sda into config file in dual-boot host
+    # Disable grub-os-prober to avoid the issue  while running
+    # grub-mkconfig
+    # Setting a flag to track whether the entry is already there in grub config
+    PROBER_DISABLED=
+    if ! grep -qe "^\s*GRUB_DISABLE_OS_PROBER=true" /etc/default/grub; then
+        PROBER_DISABLED=true
+        echo 'GRUB_DISABLE_OS_PROBER=true' >> /etc/default/grub
+    fi
+
     $GRUB_MKCONFIG
 
+    # Remove the fix to disable os_prober
+    if [ -n "$PROBER_DISABLED" ]; then
+        sed -i '$d' /etc/default/grub
+    fi
+
     RELEASE=`lsb_release -cs`
     [ -n "$RELEASE" ]
     # grub-mkconfig generates a config with the device in it,