scripts/record_bag.py: change the default stop signal from SIGTERM to SIGINT

* when SIGTERM is used the last record file is incomplete and error is shown
  when trying to play or show info on it:
  E1026 16:23:16.325891 40186 record_file_reader.cc:88] [cyber_recorder] Record file is not complete.

* instead of changing every record_bag.py --stop call:
  docs/howto/how_to_run_MSF_localization_module_on_your_local_computer.md:python /apollo/scripts/record_bag.py --stop
  docs/howto/how_to_run_MSF_localization_module_on_your_local_computer_cn.md:python /apollo/scripts/record_bag.py --stop
  docs/howto/how_to_run_NDT_localization_module_on_your_local_computer_cn.md:python ./scripts/record_bag.py --stop
  modules/dreamview/conf/hmi_modes/ipc1_mkz_close_loop.pb.txt:    stop_command: "/apollo/scripts/record_bag.py --stop"
  modules/dreamview/conf/hmi_modes/ipc1_mkz_standard_debug.pb.txt:    stop_command: "/apollo/scripts/record_bag.py --stop"
  modules/dreamview/conf/hmi_modes/mkz_close_loop.pb.txt:    stop_command: "/apollo/scripts/record_bag.py --stop"
  modules/dreamview/conf/hmi_modes/mkz_standard_debug.pb.txt:    stop_command: "/apollo/scripts/record_bag.py --stop"
  modules/dreamview/conf/hmi_modes/navigation.pb.txt:    stop_command: "/apollo/scripts/record_bag.py --stop"
  modules/dreamview/conf/hmi_modes/rtk.pb.txt:    stop_command: "/apollo/scripts/record_bag.py --stop"
  modules/dreamview/conf/hmi_modes/vehicle_calibration.pb.txt:    stop_command: "/apollo/scripts/record_bag.py --stop --stop_signal SIGINT"

  like upstream did for some of them in:

  commit 4d428a30
  Author: SeasoulChris <274224843@qq.com>
  Date:   Wed Jul 15 20:43:49 2020 +0800

    change recorder stop_signal to SIGINT

  lets change the default value, as it's not clear why SIGTERM was used
  in first place

scripts/record_bag.py

@@ -102,7 +102,7 @@ class ArgManager(object):
                                  'that case, the False value is ignored.')
         self.parser.add_argument('--stop', default=False, action="store_true",
                                  help='Stop recorder.')
-        self.parser.add_argument('--stop_signal', default="SIGTERM",
+        self.parser.add_argument('--stop_signal', default="SIGINT",
                                  help='Signal to stop the recorder.')
         self.parser.add_argument('--all', default=False, action="store_true",
                                  help='Record all topics even without high '