Adjust master_gen.PopulateBuildmasterConfig() to look at master_site_config

scripts/tools/buildbot_tool_templates/tryserver/master.cfg

Index: scripts/tools/buildbot_tool_templates/tryserver/master.cfg
diff --git a/scripts/tools/buildbot_tool_templates/tryserver/master.cfg b/scripts/tools/buildbot_tool_templates/tryserver/master.cfg
index 5e9b63098a08b9cbd4f4318d807368969a596719..0f57f445437e8f5b670947c852fc9c5d445a3639 100644
--- a/scripts/tools/buildbot_tool_templates/tryserver/master.cfg
+++ b/scripts/tools/buildbot_tool_templates/tryserver/master.cfg
@@ -6,6 +6,8 @@
 
 import os
 
+import master_site_config
+
 # This module comes from scripts/, which must be in the PYTHONPATH.
 from master import master_gen
 
@@ -16,4 +18,5 @@ BuildmasterConfig = {}
 
 master_gen.PopulateBuildmasterConfig(
     BuildmasterConfig,
-    os.path.join(os.path.dirname(os.path.abspath(__file__)), 'builders.pyl'))
+    os.path.join(os.path.dirname(os.path.abspath(__file__)), 'builders.pyl'),
+    master_site_config.%(master_classname)s)