Fix on log and metric issue on Windows when using pytorch with multithread (#3604)

Co-authored-by: veraku <shuchengfang@outlook.com>

nni/runtime/log.py

@@ -88,7 +88,7 @@ def _init_logger_dispatcher() -> None:
 
 def _init_logger_trial() -> None:
     log_path = _prepare_log_dir(trial_env_vars.NNI_OUTPUT_DIR) / 'trial.log'
-    log_file = open(log_path, 'w')
+    log_file = open(log_path, 'a')
     _register_handler(StreamHandler(log_file), logging.INFO)
 
     if trial_env_vars.NNI_PLATFORM == 'local':

nni/runtime/platform/local.py

@@ -13,7 +13,7 @@ from nni.utils import to_json
 _sysdir = trial_env_vars.NNI_SYS_DIR
 if not os.path.exists(os.path.join(_sysdir, '.nni')):
     os.makedirs(os.path.join(_sysdir, '.nni'))
-_metric_file = open(os.path.join(_sysdir, '.nni', 'metrics'), 'wb')
+_metric_file = open(os.path.join(_sysdir, '.nni', 'metrics'), 'ab')
 
 _outputdir = trial_env_vars.NNI_OUTPUT_DIR
 if not os.path.exists(_outputdir):