Move watchlog module into isctest.log package

Preparation for further logging improvements - keep the watchlog
contents in a separate module inside isctest.log. Export the names in
the log package so the imports don't change for the users of these
classes.

bin/tests/system/isctest/log/__init__.py

@@ -0,0 +1,12 @@
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0.  If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+from .watchlog import LogFile, WatchLogFromStart, WatchLogFromHere

bin/tests/system/isctest/log/watchlog.py

@@ -9,12 +9,10 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
-from typing import Iterator, Optional, TextIO, Dict, Any, overload, List, Union
+from typing import Iterator, Optional, TextIO, Dict, Any
 
 import abc
 import os
-import shlex
-import subprocess
 import time