Add tool to trigger builders on a specific commit.

You can

Trigger all master bots on a given commit:
tools/trigger.py d33415efca832aa9ad92998f3edfc1b4466dccd5

Trigger all release bots on a given commit:
tools/trigger.py d33415efca832aa9ad92998f3edfc1b4466dccd5 --release

Trigger a specific master bot on a given commit:
tools/trigger.py d33415efca832aa9ad92998f3edfc1b4466dccd5 --builder linux-android-6.0.1

Trigger a specific release bot on a given commitL
tools/trigger.py d33415efca832aa9ad92998f3edfc1b4466dccd5 --builder linux-android-6.0.1 --release

Change-Id: I1904326328f840d67c748a4ae6b076b68913b03f
diff --git a/infra/config/global/luci-scheduler.cfg b/infra/config/global/luci-scheduler.cfg
index 1b61b86..42d7e46 100644
--- a/infra/config/global/luci-scheduler.cfg
+++ b/infra/config/global/luci-scheduler.cfg
@@ -16,6 +16,8 @@
   }
 }
 
+# The format of this file is important, we have a hackish parsing to trigger
+# builds in tools/trigger.py
 trigger {
   id: "master-gitiles-trigger"
   acl_sets: "default"