sgi/build-test-buildroot: pack kvm-unit-tests and kvmtool in disk image

Add kvm-unit-tests directory and kvmtool (lkvm) binary in the ext3
parition of buildroot disk image.

Signed-off-by: Sathyam Panda <sathyam.panda@arm.com>
Change-Id: I8b9fc819f64a1b4c649f0c7ed5557589fa5d2bd8