management: Fix recent argument parsing regressions.

Fixes a regression introduced in
fbdf539bf2.

zerver/management/commands/fill_memcached_caches.py

@@ -7,7 +7,7 @@ from django.core.management.base import BaseCommand
 from zerver.lib.cache_helpers import fill_remote_cache, cache_fillers
 
 class Command(BaseCommand):
-    def parse_arguments(self, parser):
+    def add_arguments(self, parser):
         # type: (ArgumentParser) -> None
         parser.add_argument('--cache', dest="cache", default=None,
                             help="Populate the memcached cache of messages.")

zerver/management/commands/initialize_voyager_db.py

@@ -31,7 +31,7 @@ def create_users(name_list, bot_type=None):
 class Command(BaseCommand):
     help = "Populate an initial database for Zulip Voyager"
 
-    def parse_arguments(self, parser):
+    def add_arguments(self, parser):
         # type: (ArgumentParser) -> None
         parser.add_argument('--extra-users',
                             dest='extra_users',

zerver/management/commands/logout_all_users.py

@@ -12,7 +12,7 @@ from zerver.models import get_realm
 class Command(BaseCommand):
     help = "Log out all users."
 
-    def parse_arguments(self, parser):
+    def add_arguments(self, parser):
         # type: (ArgumentParser) -> None
         parser.add_argument('--realm',
                             dest='realm',