[Android] Add context manager to record logcat during step(s).

scripts/slave/recipes/cronet.expected/android_cronet_builder.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os, sys\n\nbuild_path = sys.argv[1]\nif os.path.exists(build_path):\n  for (path, dir, files) in os.walk(build_path):\n    for cur_file in files:\n      if cur_file.endswith('index.lock'):\n        path_to_file = os.path.join(path, cur_file)\n        print 'deleting %s' % path_to_file\n        os.remove(path_to_file)\n",
       "[SLAVE_BUILD]"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "cleanup index.lock",
@@ skipping 211 matching lines @@
       "android-cronet"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "sizes"
   },
   {
     "cmd": [
       "[BUILD]/scripts/slave/daemonizer.py",
       "--",
       "[SLAVE_BUILD]/src/build/android/adb_logcat_monitor.py",
-      "[SLAVE_BUILD]/src/out/logcat"
+      "[SLAVE_BUILD]/src/out/logcat_dir"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
     "name": "spawn_logcat_monitor"
   },
   {
     "cmd": [
       "python",
@@ skipping 257 matching lines @@
     "name": "shutdown_device_monitor"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/tee.py",
       "[SLAVE_BUILD]/src/out/Release/full_log",
       "--",
       "[SLAVE_BUILD]/src/build/android/adb_logcat_printer.py",
-      "[SLAVE_BUILD]/src/out/logcat"
+      "[SLAVE_BUILD]/src/out/logcat_dir"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "logcat_dump"
   },
   {
     "cmd": [
       "[SLAVE_BUILD]/src/third_party/android_platform/development/scripts/stack",
       "--arch",
       "arm",
       "--more-info",
@@ skipping 37 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]