Introduce a stumpy-pre-flight-branch target in cbuildbot.

TEST=cbuildbot_config_unittest
BUG=chrome-os-partner:4695
diff --git a/buildbot/cbuildbot_config.py b/buildbot/cbuildbot_config.py
index 2d33fa5..84d5fa6 100644
--- a/buildbot/cbuildbot_config.py
+++ b/buildbot/cbuildbot_config.py
@@ -527,6 +527,21 @@
   'push_overlays': 'both',
 }])
 
+add_config('stumpy-pre-flight-branch', [internal, {
+  'board' : 'stumpy',
+  'master' : True,
+
+  'uprev' : True,
+  'overlays': 'both',
+  'push_overlays': 'both',
+  'build_tests' : False,
+  'unittests' : False,
+  'vm_tests' : False,
+  'prebuilts' : True,
+  'git_sync': True,
+  'binhost_key': 'FULL_BINHOST',
+}])
+
 add_config('x86-mario-pre-flight-branch', [internal, {
   'board' : 'x86-mario',
   'master' : True,