cmds: Permit multiple --overlays
Extend commands that support passing an --overlay (build, clean, process, run) to permit multiple. The left-most --overlay is the lowest overlay layer, and the right-most is the highest.
This allows this sort of thing:
shrinkwrap build ns-edk2.yaml -o arch/v9.3.yaml -o myete.yaml -o mycustom.yaml
Signed-off-by: Ryan Roberts ryan.roberts@arm.com