attempt to stabilize c00040.vtc (for travis arm tests)

We should not consider an early close of the backend connection a
failure of the test, this vtc is not concerned with bodies.

bin/varnishtest/tests/c00040.vtc

@@ -35,6 +35,7 @@ server s1 {
 	send "1...5: ..0....5....0....5....0\r\n"
 	send "1...5: ..0....5....0....5....0\r\n"
 	send "1...5: ..0....5....0....5...\r\n\r\n"
+	non_fatal
 	send "asdf"
 
 	rxreq
@@ -48,6 +49,7 @@ server s1 {
 	send "1...5: ..0....5....0....5....0\r\n"
 	send "1...5: ..0....5....0....5....0\r\n"
 	send "1...5: ..0....5....0....5....\r\n\r\n"
+	non_fatal
 	send "asdf"
 } -start