Tests: added stream $session_time test.

While here, adjusted configuration to provide non-zero values.
diff --git a/stream_access_log.t b/stream_access_log.t
index 0df1636..a354da6 100644
--- a/stream_access_log.t
+++ b/stream_access_log.t
@@ -43,7 +43,7 @@
     log_format  byte  $bytes_received:$bytes_sent:
                       $upstream_bytes_sent:$upstream_bytes_received;
     log_format  time  $upstream_connect_time:$upstream_first_byte_time:
-                      $upstream_session_time;
+                      $upstream_session_time:$session_time;
 
     access_log  %%TESTDIR%%/off.log test;
 
@@ -61,6 +61,7 @@
     server {
         listen      127.0.0.1:8082;
         proxy_pass  127.0.0.1:8080;
+        proxy_download_rate 2;
         access_log  %%TESTDIR%%/time.log time;
     }
 
@@ -164,7 +165,7 @@
 	'log addr');
 like($t->read_file('date.log'), qr#^\d+.\d+![-+\w/: ]+![-+\dT:]+$#, 'log date');
 is($t->read_file('byte.log'), "8:3:8:3\n", 'log bytes');
-like($t->read_file('time.log'), qr/0\.\d{3}:0\.\d{3}:0\.\d{3}/, 'log time');
+like($t->read_file('time.log'), qr/0\.\d+:0\.\d+:1\.\d+:1\.\d+/, 'log time');
 
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