Tests: fixed stream js exit tests introduced in 69d71a15d407.

Previously, the tests relied upon the following assumption: two
consecutive syswrite() in stream_daemon will be received as a single
data chunk in stream which is not always the case.

stream_js_exit.t

diff --git a/stream_js_exit.t b/stream_js_exit.t
index 5b926a4..257562c 100644
--- a/stream_js_exit.t
+++ b/stream_js_exit.t
@@ -69,8 +69,6 @@
 
 EOF
 
-my $p = port(8080);
-
 $t->write_file('test.js', <<EOF);
     function test_njs(r) {
         r.return(200, njs.version);
@@ -140,10 +138,11 @@
 
 		log2i("$client $buffer");
 
+		$buffer = $buffer . $buffer;
+
 		log2o("$client $buffer");
 
 		$client->syswrite($buffer);
-		$client->syswrite($buffer);
 
 		close $client;
 	}