Reuse parsoid varnish for restbase

Authored by akosiaris.


Reuse parsoid varnish for restbase

The idea is to rely on the Host header to distinguish between
parsoid and restbase, and reassign the req.backend variable rather late on
the vcl_recv in order to do the minimal possible changes in vcl.
Rely on a terminating return statement to avoid clamping the host
header and the rest of the parsoid code in vcl_recv. Avoid cache lookup and

Bug: T78194
Change-Id: Ifed6cc7ebc292b6678fca28f874c8ca7840a94d9