Switch UI builders to system image branches

Change-Id: Ia923e42a2378f3e34f138fec259278e7849fab8e
diff --git a/build/masters/master.client.adt/builders.pyl b/build/masters/master.client.adt/builders.pyl
index 376b493..0be2f7a 100644
--- a/build/masters/master.client.adt/builders.pyl
+++ b/build/masters/master.client.adt/builders.pyl
@@ -197,7 +197,7 @@
      "UI": {
        "name": "emulator ui test",
        "id": "_5",
-       "scheduler": "ui_scheduler",
+       "scheduler": "system_image_scheduler",
      },
      "Console": {
        "name": "emulator console test",