python: Sort imports with isort.

Fixes #2665.

Regenerated by tabbott with `lint --fix` after a rebase and change in
parameters.

Note from tabbott: In a few cases, this converts technical debt in the
form of unsorted imports into different technical debt in the form of
our largest files having very long, ugly import sequences at the
start.  I expect this change will increase pressure for us to split
those files, which isn't a bad thing.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/test_runner.py

@@ -1,38 +1,33 @@
-from functools import partial
+import os
 import random
+import shutil
 import sys
-
-from typing import Any, Callable, Dict, List, Optional, Set, Tuple, \
-    Type, TypeVar, Union
+import time
+import unittest
+from functools import partial
+from multiprocessing.sharedctypes import Synchronized
+from typing import Any, Callable, Dict, List, Optional, Set, Tuple, Type, TypeVar, Union
 from unittest import loader, runner
 from unittest.result import TestResult
 
 from django.conf import settings
-from django.db import connections, ProgrammingError
-from django.urls.resolvers import URLPattern
+from django.db import ProgrammingError, connections
 from django.test import TestCase
 from django.test import runner as django_runner
 from django.test.runner import DiscoverRunner
 from django.test.signals import template_rendered
+from django.urls.resolvers import URLPattern
 
+from scripts.lib.zulip_tools import (
+    TEMPLATE_DATABASE_DIR,
+    get_dev_uuid_var_path,
+    get_or_create_dev_uuid_var_path,
+)
 from zerver.lib import test_helpers
 from zerver.lib.cache import bounce_key_prefix_for_testing
 from zerver.lib.rate_limiter import bounce_redis_key_prefix_for_testing
 from zerver.lib.sqlalchemy_utils import get_sqlalchemy_connection
-from zerver.lib.test_helpers import (
-    write_instrumentation_reports,
-    append_instrumentation_data,
-)
-
-import os
-import time
-import unittest
-import shutil
-
-from multiprocessing.sharedctypes import Synchronized
-
-from scripts.lib.zulip_tools import get_dev_uuid_var_path, TEMPLATE_DATABASE_DIR, \
-    get_or_create_dev_uuid_var_path
+from zerver.lib.test_helpers import append_instrumentation_data, write_instrumentation_reports
 
 # We need to pick an ID for this test-backend invocation, and store it
 # in this global so it can be used in init_worker; this is used to