Fix iperf test and make server/client jobs to write to different result log directory.

Change-Id: Ia7cb8be7e3a25f28c34a8302044cfa530b10ed05

BUG=None
TEST=run it through autoserv.

Review URL: http://codereview.chromium.org/6902127
diff --git a/server/tests/netpipe/netpipe.py b/server/tests/netpipe/netpipe.py
index 3b3bdc7..33d075f 100644
--- a/server/tests/netpipe/netpipe.py
+++ b/server/tests/netpipe/netpipe.py
@@ -38,9 +38,11 @@
                                           buffer, upper_bound, variance)
 
         server_command = subcommand.subcommand(server_at.run,
-                                    [server_control_file, server.hostname])
+                                    [server_control_file, server.hostname],
+                                    subdir='server')
         client_command = subcommand.subcommand(client_at.run,
-                                    [client_control_file, client.hostname])
+                                    [client_control_file, client.hostname],
+                                    subdir='client')
 
         subcommand.parallel([server_command, client_command])