Lightweight devserver.

By default, devserver runs with 2 threads instead of the default 10.
If more threads are needed, devserver should be started in production
mode.

BUG=chromium:260477
TEST=cbuildbot --remote on lumpy-release

Change-Id: I4688c2f582fe84a1f9676c5b887989f6382406ec
Reviewed-on: https://gerrit.chromium.org/gerrit/62436
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Joy Chen <joychen@chromium.org>
Reviewed-by: Joy Chen <joychen@chromium.org>
Tested-by: Joy Chen <joychen@chromium.org>
diff --git a/devserver.py b/devserver.py
index a80046b..faec8a1 100755
--- a/devserver.py
+++ b/devserver.py
@@ -151,6 +151,7 @@
                     'response.timeout': 6000,
                     'request.show_tracebacks': True,
                     'server.socket_timeout': 60,
+                    'server.thread_pool': 2,
                   },
                   '/api':
                   {