(on the physical node the tmcd request is coming from) look for a
VNODE= tag in the request (similar in operation to VERSION=). If there
is a vnode tag, then check for that mapping (in the nodes table). The
vnode must map to the physical node making the request (in iptonodeid()).
If so, replace the nodeid with the vnodeid for the remainder of the
session. Currently no permission checking, so a vnode could ask for
another vnode's account data (on the same physical node of course). At
some point we need to either generate per vnode certs (perhaps on the
fly) or just cons of a secret key and pass it over. Not going to worry
about it for now, since the only people who will be allowed to
allocate virtual nodes are trusted anyway.