CrOS: Use local Chromite checkout for configs.

scripts/slave/recipes/cros/cbuildbot_tryjob.expected/external.json

Index: scripts/slave/recipes/cros/cbuildbot_tryjob.expected/external.json
diff --git a/scripts/slave/recipes/cros/cbuildbot_tryjob.expected/basic.json b/scripts/slave/recipes/cros/cbuildbot_tryjob.expected/external.json
similarity index 77%
rename from scripts/slave/recipes/cros/cbuildbot_tryjob.expected/basic.json
rename to scripts/slave/recipes/cros/cbuildbot_tryjob.expected/external.json
index 755b197384feb1d0ca7771f25b3f7769a6725cc9..b983bc0b8750ba82e0c43afd3f68dcfd63205aa2 100644
--- a/scripts/slave/recipes/cros/cbuildbot_tryjob.expected/basic.json
+++ b/scripts/slave/recipes/cros/cbuildbot_tryjob.expected/external.json
@@ -47,6 +47,23 @@
     "name": "checkout chromite branch [master]"
   },
   {
+    "cmd": [
+      "python",
+      "-u",
+      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
+      "[SLAVE_BUILD]/chromite/cbuildbot/config_dump.json",
+      "/path/to/tmp/json"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "read chromite config",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@config@{@@@",
+      "@@@STEP_LOG_LINE@config@  \"x86-generic-full\": {}@@@",
+      "@@@STEP_LOG_LINE@config@}@@@",
+      "@@@STEP_LOG_END@config@@@"
+    ]
+  },
+  {
     "allow_subannotations": true,
     "cmd": [
       "[SLAVE_BUILD]/chromite/bin/cbuildbot",