scripts: twister_blackbox: Added the ability to clear log from the code

@pytest.fixture

def clear_log():

    # clear_log is used by pytest fixture

    # However, clear_log_in_test is prepared to be used directly in the code, wherever required

    clear_log_in_test()

def clear_log_in_test():

    # Required to fix the pytest logging error

    # See: https://github.com/pytest-dev/pytest/issues/5502

    loggers = [logging.getLogger()] \

"""

Blackbox tests for twister's command line functions

"""

import logging

import importlib

import mock

import os

import pytest

import sys

from conftest import ZEPHYR_BASE, testsuite_filename_mock

from conftest import ZEPHYR_BASE, testsuite_filename_mock, clear_log_in_test

from twisterlib.testplan import TestPlan

sys.path.insert(0, os.path.join(ZEPHYR_BASE, "scripts/pylib/twister/twisterlib"))

                        os.remove(path)

                    assert str(sys_exit.value) == '0'

                    loggers = [logging.getLogger()] + \

                              list(logging.Logger.manager.loggerDict.values()) + \

                              [logging.getLogger(name) for \

                               name in logging.root.manager.loggerDict]

                    for logger in loggers:

                        handlers = getattr(logger, 'handlers', [])

                        for handler in handlers:

                            logger.removeHandler(handler)

                    clear_log_in_test()

    @pytest.mark.parametrize(

        ('manufacturer', 'product', 'serial', 'runner'),