seldon does not check for container connectivity on config changed

[beliaev-maksim]

charm goes into error state when "config changed" is called

unit-seldon-controller-manager-0: 04:44:24 ERROR unit.seldon-controller-manager/0.juju-log Uncaught exception while in charm code:
Traceback (most recent call last):
  File "/usr/lib/python3.8/urllib/request.py", line 1354, in do_open
    h.request(req.get_method(), req.selector, req.data, headers,
  File "/usr/lib/python3.8/http/client.py", line 1256, in request
    self._send_request(method, url, body, headers, encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1302, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1251, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1011, in _send_output
    self.send(msg)
  File "/usr/lib/python3.8/http/client.py", line 951, in send
    self.connect()
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/pebble.py", line 252, in connect
    self.sock.connect(self.socket_path)
FileNotFoundError: [Errno 2] No such file or directory

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/pebble.py", line 1484, in _request_raw
    response = self.opener.open(request, timeout=self.timeout)
  File "/usr/lib/python3.8/urllib/request.py", line 525, in open
    response = self._open(req, data)
  File "/usr/lib/python3.8/urllib/request.py", line 542, in _open
    result = self._call_chain(self.handle_open, protocol, protocol +
  File "/usr/lib/python3.8/urllib/request.py", line 502, in _call_chain
    result = func(*args)
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/pebble.py", line 266, in http_open
    return self.do_open(_UnixSocketConnection, req,  # type:ignore
  File "/usr/lib/python3.8/urllib/request.py", line 1357, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error [Errno 2] No such file or directory>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "./src/charm.py", line 528, in <module>
    main(SeldonCoreOperator)
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/main.py", line 436, in main
    _emit_charm_event(charm, dispatcher.event_name)
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/main.py", line 144, in _emit_charm_event
    event_to_emit.emit(*args, **kwargs)
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/framework.py", line 354, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/framework.py", line 830, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/framework.py", line 919, in _reemit
    custom_handler(event)
  File "./src/charm.py", line 511, in _on_event
    self._update_layer()
  File "./src/charm.py", line 260, in _update_layer
    current_layer = self.container.get_plan()
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/model.py", line 1933, in get_plan
    return self._pebble.get_plan()
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/pebble.py", line 1772, in get_plan
    resp = self._request('GET', '/v1/plan', {'format': 'yaml'})
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/pebble.py", line 1451, in _request
    response = self._request_raw(method, path, query, headers, data)
  File "/var/lib/juju/agents/unit-seldon-controller-manager-0/charm/venv/ops/pebble.py", line 1497, in _request_raw
    raise ConnectionError(e.reason)
ops.pebble.ConnectionError: [Errno 2] No such file or directory