sgi/prepare-fedora-disk: automate fedora disk preparation for ras and kvm test

Add support for preparing fedora disk for ras test by adding the sgi linux
kernel entry in the fedora grub menu. Add support for kvm test by downloading
and packaging lkvm executable in root directory of fedora disk.

This script needs sudo permission for mouting the disk image and expects a
installed fedora disk image in prebuilts/sgi folder.

Change-Id: I3cb1ea72b9e77b7b1a78c8568a6d66d7f40e2883
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>