auth_authenticate_newcache: prefer non-V4ROOT export over V4ROOT exports

Currently auth_authenticate_internal finds an export and if it
is a V4ROOT export, it reports that there is no match.  Unlike
lookup_export() it doesn't keep looking for an acceptable export.

So remove the test from auth_authenticate_internal(), and add it to
auth_authenticate_newcache(), where the search can be allowed to
continue.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Steve Dickson <steved@redhat.com>