Attempt to fix r03996 on systems without massive resources

It's amazing how long time it takes to find a delay of half a second...

bin/varnishtest/tests/r03996.vtc

@@ -17,6 +17,7 @@ varnish v1 -vcl+backend {
 	import vtc;
 
 	sub vcl_recv {
+		vtc.sleep(0.5s);
 		if (req.http.barrier) {
 			vtc.barrier_sync(req.http.barrier);
 		}
@@ -25,6 +26,8 @@ varnish v1 -vcl+backend {
 
 } -start
 
+varnish v1 -vsl_catchup
+
 client c1 {
 	stream 0 {
 		rxgoaway
@@ -43,6 +46,8 @@ client c1 {
 	stream 0 -wait
 } -run
 
+varnish v1 -vsl_catchup
+
 varnish v1 -expect sc_rapid_reset == 1
 
 varnish v1 -cliok "param.set feature -vcl_req_reset"
@@ -64,4 +69,6 @@ client c2 {
 	stream 0 -wait
 } -run
 
+varnish v1 -vsl_catchup
+
 varnish v1 -expect sc_rapid_reset == 2