Run the following from the host:

    vboxmanage debugvm "${VM_NAME}" dumpguestcore --filename tails.dump

and that's it.

VirtualBox' VM core is an ELF that contains [some headers and other
state](http://www.virtualbox.org/manual/ch12.html#guestcoreformat) of
the Tails guest in addition to the memory dump, but there's no
reasonable possibility of finding the pattern as false positives there
so there's no reason to bother cutting the headers away.
