stabilize timing-sensitive test

There are two one-second delays on the server side, but varnishd might
read the response a bit longer after the first delay such that the
second interval is shortened from the varnish perspective.

bin/varnishtest/tests/s00004.vtc

@@ -37,7 +37,7 @@ logexpect l1 -v v1 -g request {
 	expect * =	Timestamp	{Start: \S+ 0\.000000 0\.000000}
 	expect * =	Timestamp	{Bereq: \S+ 0\.\d+ 0\.\d+}
 	expect * =	Timestamp	{Beresp: \S+ 1\.\d+ [01]\.\d+}
-	expect * =	Timestamp	{BerespBody: \S+ 2\.\d+ 1\.\d+}
+	expect * =	Timestamp	{BerespBody: \S+ 2\.\d+ (1\.\d+|0\.9)}
 	expect * =	End
 	expect 0 1003	Begin		{req 1001 restart}
 	expect * =	Timestamp	{Start: \S+ 2\.\d+ 0\.\d+}