Bug#1040899: debian-cd: "Failed to mount /target/proc" during GRUB installation

["arizona.rover" <arizona.rover@protonmail.com>]

syslog reactivated using instructions from #1039710

Jul 19 08:24:08 main-menu[256]: INFO: Menu item 'grub-installer' selected
Jul 19 08:24:08 Success mounting /target/proc
Jul 19 08:24:08 Success mounting /target/sys
Jul 19 08:24:09 error: Error creating /target/sys/firmware/efi/efivars
Jul 19 08:24:49 (process:5127): mkdir: can't create directory '/target/sys/firmware/efi': Operation not permitted
Jul 19 08:24:49 main-menu[256]: WARNING **: Configuring 'grub-installer' failed with error code 1
Jul 19 08:24:49 main-menu[256]: WARNING **: Menu item 'grub-installer' failed