Fixed several flake8 errors

django/core/management/commands/squashmigrations.py

-import sys
-
 from django.core.management.base import BaseCommand, CommandError
 from django.utils import six
 from django.db import connections, DEFAULT_DB_ALIAS, migrations

tests/admin_scripts/management/commands/base_command.py

@@ -7,9 +7,9 @@ class Command(BaseCommand):
 
     def add_arguments(self, parser):
         parser.add_argument('args', nargs='*')
-        parser.add_argument('--option_a', '-a',  default='1')
-        parser.add_argument('--option_b', '-b',  default='2')
-        parser.add_argument('--option_c', '-c',  default='3')
+        parser.add_argument('--option_a', '-a', default='1')
+        parser.add_argument('--option_b', '-b', default='2')
+        parser.add_argument('--option_c', '-c', default='3')
 
     def handle(self, *labels, **options):
         print('EXECUTE:BaseCommand labels=%s, options=%s' % (labels, sorted(options.items())))

tests/user_commands/management/commands/optparse_cmd.py

 from optparse import make_option
 
-from django.core.management.base import BaseCommand, CommandError
+from django.core.management.base import BaseCommand
 
 
 class Command(BaseCommand):
@@ -13,7 +13,7 @@ class Command(BaseCommand):
     )
 
     def handle(self, *args, **options):
-        example = options["example"]
+        options["example"]
         # BaseCommand default option is available
         options['verbosity']
         self.stdout.write("All right, let's dance %s." % options["style"])