[autotest] Separate the logs deployment logs

Instead flush all the logs into console, write the logs of every server
into a log file in a single thread. In this way, we can save the log for
debug purpose and all the logs will not be mixed up.

BUG=chromium:666101
TEST=unittest and test in a test server.

Change-Id: Iaf7b303f0c3b0c9346c5346052ba07c79d2fb990
Reviewed-on: https://chromium-review.googlesource.com/435503
Commit-Ready: Shuqian Zhao <shuqianz@chromium.org>
Tested-by: Shuqian Zhao <shuqianz@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
diff --git a/site_utils/lib/infra.py b/site_utils/lib/infra.py
index 4fb8ffb..421c370 100644
--- a/site_utils/lib/infra.py
+++ b/site_utils/lib/infra.py
@@ -114,7 +114,8 @@
         @raises CalledProcessError: If there was a non-0 return code.
         """
         out = subprocess.check_output(['googlesh', '-s', '-uchromeos-test',
-                                       '-m%s' % host, '%s' % cmd])
+                                       '-m%s' % host, '%s' % cmd],
+                                      stderr=subprocess.STDOUT)
         return out
     return runner