adb: move known devices file under cache so it works with remote_run (attempt #2)

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_android_n6.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "tryserver.webrtc",
       "--builder",
       "android_n6",
@@ skipping 241 matching lines @@
   {
     "cmd": [
       "[SLAVE_BUILD]/src/build/android/buildbot/bb_device_status_check.py",
       "--adb-path",
       "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools/adb",
       "--blacklist-file",
       "[SLAVE_BUILD]/src/out/bad_devices.json",
       "--json-output",
       "/path/to/tmp/json",
       "--known-devices-file",
-      "[BUILD]/site_config/.known_devices"
+      "[CACHE]/known_android_devices"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
     "name": "device_status_check",
     "~followup_annotations": [
       "@@@STEP_TEXT@Online devices: 1@@@",
       "@@@STEP_LOG_LINE@json.output@[@@@",
       "@@@STEP_LOG_LINE@json.output@  {@@@",
@@ skipping 451 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]