Wait for the "fast-expire" zone to be transferred

Wait for the "fast-expire" zone to be transferred

In order for a "fast-expire/IN: response-policy zone expired" message to
be logged in ns3/named.run, the "fast-expire" zone must first be
transferred in by that server.  However, with unfavorable timing, ns3
may be stopped before it manages to fetch the "fast-expire" zone from
ns5 and after the latter has been reconfigured to no longer serve that
zone.  In such a case, the "rpz" system test will report a false
positive for the relevant check.  Prevent that from happening by
ensuring ns3 manages to transfer the "fast-expire" zone before getting
shut down.

(cherry picked from commit 39191052ad90da2418f2d144708d09b12c173ec4)