kunit: tool: fix unit test cleanup handling

stable inclusion
from stable-5.10.20
commit ecb23b97a70b89054926dbf87e1bd22864236a1a
bugzilla: 50608

--------------------------------

[ Upstream commit cfd607e4 ]

* Stop leaking file objects.
* Use self.addCleanup() to ensure we call cleanup functions even if
setUp() fails.
* use mock.patch.stopall instead of more error-prone manual approach

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Tested-by: Brendan Higgins <brendanhiggins@google.com>
Acked-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>