kunit: tool: misc fixes (unused vars, imports, leaked files)

Drop some variables in unit tests that were unused and/or add assertions
based on them.

For ExitStack, it was imported, but the `es` variable wasn't used so it
didn't do anything, and we were leaking the file objects.
Refactor it to just use nested `with` statements to properly close them.

And drop the direct use of .close() on file objects in the kunit tool
unit test, as these can be leaked if test assertions fail.

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/kunit/kunit_kernel.py

@@ -14,10 +14,6 @@ import shutil
 import signal
 from typing import Iterator, Optional, Tuple
 
-from contextlib import ExitStack
-
-from collections import namedtuple
-
 import kunit_config
 import kunit_parser
 import qemu_config
@@ -168,10 +164,10 @@ class LinuxSourceTreeOperationsUml(LinuxSourceTreeOperations):
 		process.wait()
 		kunit_parser.print_with_timestamp(
 			'Disabling broken configs to run KUnit tests...')
-		with ExitStack() as es:
-			config = open(get_kconfig_path(build_dir), 'a')
-			disable = open(BROKEN_ALLCONFIG_PATH, 'r').read()
-			config.write(disable)
+
+		with open(get_kconfig_path(build_dir), 'a') as config:
+			with open(BROKEN_ALLCONFIG_PATH, 'r') as disable:
+				config.write(disable.read())
 		kunit_parser.print_with_timestamp(
 			'Starting Kernel with all configs takes a few minutes...')