Installer should not default to installing grub on /dev/mmcblk0

[Aaron Murphy]

Installing ubuntu alongside windows 10 and I had an SD card in my PC. It wouldn't boot into ubuntu on restart because it tried to install grub on mmcblk0 instead of the windows boot partition

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubiquity 2.18.8.13
ProcVersionSignature: Ubuntu 4.4.0-31.50~14.04.1-generic 4.4.13
Uname: Linux 4.4.0-31-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CasperVersion: 1.340.2
Date: Mon Oct 31 20:53:15 2016
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash --- maybe-ubiquity
LiveMediaBuild: Ubuntu 14.04.5 LTS "Trusty Tahr" - Release amd64 (20160803)
ProcEnviron:
 LANGUAGE=en_GB.UTF-8
 TERM=linux
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Will Cooke (willcooke)]

This bug, or one like it, is still present in 17.10. Trying to install Ubuntu with an SD card in the drive results in the installer trying to install grub on the sd card and failing:

"Executing 'grub-install /dev/mmcblk0' failed. This is a fatal error"

Using the custom partitioning tool confirms that grub is trying to be installed on the sd card.

[Will Cooke (willcooke)]

Actually, this is a dupe of lp:#1480703