Use request.start and end
Without the start and end we die on 'assert self.in_request' in the
core per request value store methods.
from django.core.management.base import NoArgsCommand
class Command(NoArgsCommand):
help = "Validates all installed models."
requires_model_validation = False
def handle_noargs(self, **options):
self.validate(display_num_errors=True)