Container Support

Backport https://pulp.plan.io/issues/8672

 [2021-04-29 16:07:13 +0000] [50888] [ERROR] Error handling request
 Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/django/db/backends/base/base.py", line 235, in _cursor
    return self._prepare_cursor(self.create_cursor(name))
  File "/usr/lib/python3.6/site-packages/django/db/backends/postgresql/base.py", line 223, in create_cursor
    cursor = self.connection.cursor()
 psycopg2.InterfaceError: connection already closed
 The above exception was the direct cause of the following exception:
 Traceback (most recent call last):
  File "/usr/lib64/python3.6/site-packages/aiohttp/web_protocol.py", line 422, in _handle_request
    resp = await self._request_handler(request)
  File "/usr/lib64/python3.6/site-packages/aiohttp/web_app.py", line 499, in _handle
    resp = await handler(request)
  File "/usr/lib/python3.6/site-packages/pulp_container/app/registry.py", line 102, in get_tag
    distribution = self._match_distribution(path)
  File "/usr/lib/python3.6/site-packages/pulpcore/content/handler.py", line 182, in _match_distribution
    return cls.distribution_model.objects.get(base_path__in=base_paths)
  File "/usr/lib/python3.6/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/django/db/models/query.py", line 402, in get
    num = len(clone)
  File "/usr/lib/python3.6/site-packages/django/db/models/query.py", line 256, in __len__
    self._fetch_all()
  File "/usr/lib/python3.6/site-packages/django/db/models/query.py", line 1242, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/usr/lib/python3.6/site-packages/django/db/models/query.py", line 55, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "/usr/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1140, in execute_sql
    cursor = self.connection.cursor()
  File "/usr/lib/python3.6/site-packages/django/db/backends/base/base.py", line 256, in cursor
    return self._cursor()
  File "/usr/lib/python3.6/site-packages/django/db/backends/base/base.py", line 235, in _cursor
    return self._prepare_cursor(self.create_cursor(name))
  File "/usr/lib/python3.6/site-packages/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/usr/lib/python3.6/site-packages/django/db/backends/base/base.py", line 235, in _cursor
    return self._prepare_cursor(self.create_cursor(name))
  File "/usr/lib/python3.6/site-packages/django/db/backends/postgresql/base.py", line 223, in create_cursor
    cursor = self.connection.cursor()
 django.db.utils.InterfaceError: connection already closed