testport: Add interactive test modes -i and -I

The -I flag may later conflict with the non-ZFS goal as it depends on the startup
automatically rolling back to the @clean snapshot to undo anything the user
has done in the jail.
It's 2013 now, use proper Dd.
lefotvers: Now that @dirrm is showing, properly trim it out when checking for known directories to ignore
bulk: Add debug msg (-vv) to list what missing dependency is causing a package to be rebuilt