try to stabilize test

Yes, we do not want to rely on timing, but I do not see how we could
test the lru_interval timer otherwise

seen in vtc:

---- v1   Not true: MAIN.n_lru_moved (0) == 1 (1)
*    top  RESETTING after ../../../../bin/varnishtest/tests/r02527.vtc
**   s1   Waiting for server (3/-1)
**   v1   Wait

bin/varnishtest/tests/r02527.vtc

@@ -18,7 +18,7 @@ client c1 {
 
 varnish v1 -expect MAIN.n_lru_moved == 0
 
-delay 1
+delay 2
 
 client c1 {
 	txreq