CrOS: Use local Chromite checkout for configs.

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromiumos.tryserver",
       "--builder",
-      "etc",
+      "paladin",
       "--slave",
       "test",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'chromite', 'url': 'https://chromium.googlesource.com/chromiumos/chromite.git'}]",
       "--root",
       "chromite",
       "--revision_mapping_file",
       "{}",
       "--output_json",
       "/path/to/tmp/json",
@@ skipping 19 matching lines @@
   {
     "cmd": [
       "git",
       "checkout",
       "master"
     ],
     "cwd": "[SLAVE_BUILD]/chromite",
     "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@  \"internal-paladin\": {@@@",
+      "@@@STEP_LOG_LINE@config@    \"internal\": true@@@",
+      "@@@STEP_LOG_LINE@config@  }@@@",
+      "@@@STEP_LOG_LINE@config@}@@@",
+      "@@@STEP_LOG_END@config@@@"
+    ]
+  },
+  {
     "allow_subannotations": true,
     "cmd": [
       "[SLAVE_BUILD]/chromite/bin/cbuildbot",
       "--buildroot",
-      "[ROOT]/cbuild/etc_master",
-      "--clobber",
+      "[ROOT]/cbuild/internal_master",
       "--timeout",
       "14400",
       "--remote-trybot",
       "--remote-version=4",
-      "xxx-fakeboard-fakebuild"
+      "internal-paladin"
     ],
-    "name": "cbuildbot [xxx-fakeboard-fakebuild]"
+    "name": "cbuildbot [internal-paladin]"
   }
 ]