bot_update (+recipe_module): treat patch download as infra failure.

scripts/slave/recipe_modules/bot_update/example.expected/tryjob_fail_patch.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "tryserver.chromium.linux",
       "--builder",
       "linux_rel",
@@ skipping 20 matching lines @@
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"log_lines\": [@@@",
       "@@@STEP_LOG_LINE@json.output@    [@@@",
       "@@@STEP_LOG_LINE@json.output@      \"patch error\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"Patch failed to apply\"@@@",
       "@@@STEP_LOG_LINE@json.output@    ]@@@",
       "@@@STEP_LOG_LINE@json.output@  ], @@@",
       "@@@STEP_LOG_LINE@json.output@  \"patch_failure\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"patch_root\": \"src\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"properties\": {}, @@@",
+      "@@@STEP_LOG_LINE@json.output@  \"return_code\": 1, @@@",

[tandrii(chromium), 2015/10/02 12:50:36]

normal error code.

       "@@@STEP_LOG_LINE@json.output@  \"root\": \"src\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"step_text\": \"Some step text\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LOG_LINE@patch error@Patch failed to apply@@@",
       "@@@STEP_LOG_END@patch error@@@",
       "@@@SET_BUILD_PROPERTY@failure_type@\"PATCH_FAILURE\"@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "import sys; sys.exit(1)"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "Patch failure",
     "~followup_annotations": [
       "step returned non-zero exit code: 1",
       "@@@STEP_TEXT@Check the bot_update step for details@@@",
       "@@@STEP_FAILURE@@@"
     ]
   },
   {
     "name": "$final_result",
     "reason": "Step('Patch failure') failed with return_code 1",
     "status_code": 1
   }
 ]