process: process log only capture stdout/stderr.

Originally, all log of the Process class are captured in log_buffer. So when dump the process log, it includes LISA log. After the change, only stdout/stderr are included.

lisa/util/process.py

@@ -214,9 +214,6 @@ def __init__(
 
         # add a string stream handler to the logger
         self.log_buffer = io.StringIO()
-        self._log_handler = logging.StreamHandler(self.log_buffer)
-        msg_only_format = logging.Formatter(fmt="%(message)s", datefmt="")
-        add_handler(self._log_handler, self._log, msg_only_format)
 
     @_retry_spawn
     def start(
@@ -252,6 +249,11 @@ def start(
         self._stdout_writer = LogWriter(logger=self.stdout_logger, level=stdout_level)
         self._stderr_writer = LogWriter(logger=self.stderr_logger, level=stderr_level)
 
+        self._log_handler = logging.StreamHandler(self.log_buffer)
+        msg_only_format = logging.Formatter(fmt="%(message)s", datefmt="")
+        add_handler(self._log_handler, self.stdout_logger, msg_only_format)
+        add_handler(self._log_handler, self.stderr_logger, msg_only_format)
+
         self._sudo = sudo
         self._nohup = nohup