rename scappy -> scap, scap -> scap-old

'scappy' is a python rewrite of the scap entrypoint script, intended as a
drop-in replacement. It works, so I'm promoting it to be the canonical scap.
But we'll retain the old scap script as 'scap-old' on a temporary basis in case
the new script introduces some regression.

Change-Id: I8fff9ba5f4488d74a560069115f0d411ef38fca9