The script to find best kernel from image (used by vm
and baremetal element) is duplicated and is not in sync
with each other. Moving the code to img-functions as a
function will reduce duplicated code and make it reusable
in future.
Since img-functions is not accessible in chroot env,
kernel selection is being moved from finalise.d to
cleanup.d in the vm element.
Change-Id: I8fbccc13a2c61a5191ef9ea5d2a8302a3e43b000
