Fixing Debian passwordless sudo & secure_path

Only add the secure path setting if it is not already present, it is
there by default in more recent Debians and you don't want it there
twice.

Also, the sed regex wasn't actually changing the %sudo line at all, this
makes sure sudo really is passwordless.
Remove cdrom from Debian apt source in cleanup.

Removes cdrom images from /etc/apt/sources.list during cleanup.
Addresses:  http://tickets.opscode.com/browse/BENTO-82