Bug#867804: cdrom: Stretch netinst CD installs grub config file incorrectly

[Hazel Russman <hazeldebian@gmail.com>]

Package: cdrom
Severity: normal
Tags: d-i

Dear Maintainer,

Debian-9.0.0-amd64-netinst.iso did not configure grub correctly. It created a configuration file in /boot/grub but
named it incorrectly (grub.cfg.new instead of grub.cfg). As a result, on rebooting, grub failed to reach a menu and 
dropped to a grub shell prompt. I was able to complete the boot process by hand using grub shell commands.

'm no expert on grub, but as far as I can see, the file contents are correct and include all four of the linux systems 
on my machine. Only the filename is wrong.

-- System Information:
Debian Release: 9.0
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-3-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)