convert: Remove /dev/mapper/osprober-linux-* devices left around by g…

…rub2

These devices can be left around by grub2 when it runs the osprober
tool after we run “/sbin/grub2-mkconfig -o /boot/grub2/grub.cfg”.
They are read-only mirrors of existing filesystems.  The problem is a
very old (and fixed) known bug in the tool:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=853163

These confuse later steps in conversion, specifically fstrim.

Reported-by: Ming Xie
Thanks: Laszlo Ersek
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2003503
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

convert/linux_bootloaders.ml

@@ -345,7 +345,14 @@ object (self)
   method remove_console = self#grub2_update_console ~remove:true
 
   method update () =
-    ignore (g#command [| grub2_mkconfig_cmd; "-o"; grub_config |])
+    ignore (g#command [| grub2_mkconfig_cmd; "-o"; grub_config |]);
+
+    (* Grub2 runs osprober which sometimes leaves around read-only
+     * device-mapper maps covering existing filesystems.  These
+     * confuse later steps (especially fstrim).  So just delete
+     * any if found. (RHBZ#2003503).
+     *)
+    ignore (g#command [| "sh"; "-c"; "rm -f /dev/mapper/osprober-linux-*" |])
 
   method get_config_file () =
     grub_config