recipe_modules/chromite: Use "build_type".

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'deps_file': '.DEPS.git', 'managed': True, 'name': 'chromite', 'url': 'https://chromium.googlesource.com/chromiumos/chromite.git'}]",
       "--patch_root",
       "chromite",
@@ skipping 51 matching lines @@
       "-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"
     ],
     "name": "read chromite config",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@config@{@@@",
       "@@@STEP_LOG_LINE@config@  \"internal-paladin\": {@@@",
       "@@@STEP_LOG_LINE@config@    \"_template\": \"paladin\", @@@",
-      "@@@STEP_LOG_LINE@config@    \"internal\": true, @@@",
-      "@@@STEP_LOG_LINE@config@    \"type\": \"paladin\"@@@",
+      "@@@STEP_LOG_LINE@config@    \"build_type\": \"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/internal_master",
       "--timeout",
       "14400",
       "--remote-trybot",
       "--remote-version=4",
       "internal-paladin"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "cbuildbot [internal-paladin]"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]