builder: Move Perl_edit module into common code.

There is no functional change.
sysprep: Add --scrub option.

This works like the option in virt-builder with the same name.
sysprep: Add a reference to virt-builder from the manual page.

The whole "COPYING AND CLONING" section really needs to be overhauled
too, but first we need to make virt-builder work properly for
customizing templates.
sysprep: Deprecate --selinux-relabel in favour of --autorelabel.

virt-builder added a --selinux-relabel option with a slightly
different meaning.

This commit keeps the old --selinux-relabel / --no-selinux-relabel
options in virt-sysprep, but deprecates them and replaces them with
--autorelabel and --no-autorelabel.