Cleanup rabbitmq queues when doing dev db rebuild.

Modified by tabbott to cleanup the argument handling in the modified
purge_queue management command.

Fixes #1335.

tools/do-destroy-rebuild-database

@@ -15,6 +15,7 @@ EOF
 
 sh "$(dirname "$0")/../scripts/setup/flush-memcached"
 
+./manage.py purge_queue --all
 ./manage.py migrate --noinput
 migration_status "var/migration_status_dev"
 ./manage.py createcachetable third_party_api_results

zerver/management/commands/purge_queue.py

@@ -5,19 +5,38 @@ from argparse import ArgumentParser
 from django.core.management.base import BaseCommand
 from django.core.management import CommandError
 from zerver.lib.queue import SimpleQueueClient
+from zerver.worker.queue_processors import get_active_worker_queues
 
 class Command(BaseCommand):
     def add_arguments(self, parser):
         # type: (ArgumentParser) -> None
-        parser.add_argument('queue_name', metavar='<queue name>', type=str,
-                            help="queue to purge")
+        parser.add_argument(dest="queue_name", type=str, nargs='?',
+                            help="queue to purge", default=None)
+        parser.add_argument('--all', dest="all", action="store_true",
+                            default=False, help="purge all queues")
 
     help = "Discards all messages from the given queue"
 
     def handle(self, *args, **options):
         # type: (*Any, **str) -> None
-        queue_name = options['queue_name']
+        def purge_queue(queue_name):
+            # type: (str) -> None
             queue = SimpleQueueClient()
             queue.ensure_queue(queue_name, lambda: None)
             queue.channel.queue_purge(queue_name)
+
+        if options['all']:
+            for queue_name in get_active_worker_queues():
+                purge_queue(queue_name)
+            print("All queues purged")
+        elif not options['queue_name']:
+            raise CommandError("Missing queue_name argument!")
+        else:
+            queue_name = options['queue_name']
+            if queue_name not in get_active_worker_queues():
+                raise CommandError("Unknown queue %s" % (queue_name,))
+
+            print("Purging queue %s" % (queue_name,))
+            purge_queue(queue_name)
+
         print("Done")