Fixed #23663 -- Initialize output streams for BaseCommand in __init__().

This helps with testability of management commands.

Thanks to trac username daveoncode for the report and to
Tim Graham and Claude Paroz for the reviews.

tests/admin_scripts/management/commands/color_command.py

@@ -1,9 +0,0 @@
-from django.core.management.base import BaseCommand
-
-
-class Command(BaseCommand):
-    help = "Test color output"
-    requires_system_checks = False
-
-    def handle(self, **options):
-        return self.style.SQL_KEYWORD('BEGIN')