fixing Zesty to use Apple boot selector

[Jack Howarth]

    Zesty 17.04 x86_64 beta 2, while producing a bootable installation
when installed on a MacPro, fails to appear in the Apple boot selector
like a Fedora 24/25 installation does. It is trivial to emulate the
Fedora approach by installing the
mactel-boot-logo_1.0-1~xenial_all.deb and
mactel-boot_0.9-1~xenial_amd64.deb packages followed by the
commands...

sudo mkdir -p /boot/efi/System/Library/CoreServices
sudo install -m 644 /usr/share/mactel-boot/SystemVersion.plist
/boot/efi/System/Library/CoreServices
sudo install -m 644 /usr/share/mactel-boot-logo/ubuntu.icns
/boot/efi/.VolumeIcon.icns
sudo echo "This file is required for booting" > /boot/efi/mach_kernel
sudo install -m 700 /boot/efi/EFI/ubuntu/grubx64.efi
/boot/efi/System/Library/CoreServices/boot.efi

This produces an installation which shows the Ubuntu icon in the
option-key boot selector on a MacPro 3,1. If Ubuntu followed this
approach used by Fedora, the installation script for updating
/boot/efi/EFI/ubuntu/grubx64.efi would have to be enhanced to install
a copy in /boot/efi/System/Library/CoreServices as boot.efi (since the
vfat partition used for /boot/efi doesn't support symlinks).
                  Jack