GN: take over CommandBuffer bot

infra/bots/recipes/swarm_test.expected/Test-Mac-Clang-MacMini6.2-GPU-HD4000-x86_64-Debug-CommandBuffer.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[SLAVE_BUILD]/skia/infra/bots/assets/skp/VERSION",
       "/path/to/tmp/"
     ],
     "name": "Get downloaded SKP VERSION"
@@ skipping 157 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@    if retry == RETRIES:@@@",
       "@@@STEP_LOG_LINE@python.inline@      raise@@@",
       "@@@STEP_LOG_LINE@python.inline@    waittime = WAIT_BASE * math.pow(2, retry)@@@",
       "@@@STEP_LOG_LINE@python.inline@    print 'Retry in %d seconds.' % waittime@@@",
       "@@@STEP_LOG_LINE@python.inline@    time.sleep(waittime)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
-      "catchsegv",
       "[SLAVE_BUILD]/out/Debug/dm",
       "--undefok",
       "--resourcePath",
       "[SLAVE_BUILD]/skia/resources",
       "--skps",
       "[SLAVE_BUILD]/skp",
       "--images",
       "[SLAVE_BUILD]/skimage/dm",
       "--colorImages",
       "[SLAVE_BUILD]/skimage/colorspace",
@@ skipping 218 matching lines @@
       ".RW2",
       "_",
       "image",
       "_",
       ".PEF",
       "_",
       "image",
       "_",
       ".SRW"
     ],
-    "env": {
-      "BUILDTYPE": "Debug",
-      "CHROME_HEADLESS": "1",
-      "SKIA_OUT": "[SLAVE_BUILD]/out"
-    },
+    "cwd": "[SLAVE_BUILD]/skia",
     "name": "dm"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]