Bug#250 Helium build fail Cause "Untrusted packages could compromise your system's security"

http://bugzilla.vyos.net/show_bug.cgi?id=250

Replace gpg key 

    rm -f livecd/config.vyatta/chroot_sources/vyatta.chroot.gpg
    wget -qO livecd/config.vyatta/chroot_sources/vyatta.chroot.gpg http://dev.packages.vyos.net/vyos-root-gpg