Fix for several veewee setup problems

It looks like there are two small issues with the veewee build of the ubuntu-7.10-server-amd64 base box. The following two changes allowed a base box to be built successfully for me.

1. The VBoxLinuxAdditions script exits with a non-zero status because there's no X11 installed. As a result, the veewee build was dying at that line and not going on. I think the non-zero exit from the script is OK, since we don't care about the X11 guest additions. The "|| true" will guarantee that the line always evaluates to true. While this works, it's probably not an ideal solution because has the chance to mask real failures as well. I hope it's OK.

2. The sudo script was not getting its executable bits set. I've put "&& chmod a+x /usr/bin/sudo" at the end of script heredoc so that it will get its executable bits set in the same shell operation as writing out the file.