poco http refuse

Remove any following parts if does not have details about

**Describe the bug**
问题是偶现的，android7.1手机，频率：20%

```
../../../.local/lib/python3.5/site-packages/poco/proxy.py:72: in wrapped
return func(proxy, *args, **kwargs)
../../../.local/lib/python3.5/site-packages/poco/proxy.py:774: in exists
return self.attr('visible')
../../../.local/lib/python3.5/site-packages/poco/proxy.py:39: in wrapped
return func(self, *args, **kwargs)
../../../.local/lib/python3.5/site-packages/poco/proxy.py:734: in attr
nodes = self._do_query(multiple=False)
../../../.local/lib/python3.5/site-packages/poco/proxy.py:872: in _do_query
self._nodes = self.poco.agent.hierarchy.select(self.query, multiple)
../../../.local/lib/python3.5/site-packages/poco/utils/retry.py:20: in wrapped
raise ex
../../../.local/lib/python3.5/site-packages/poco/utils/retry.py:15: in wrapped
return func(*args, **kwargs)
../../../.local/lib/python3.5/site-packages/poco/utils/hrpc/hierarchy.py:33: in select
return self.selector.select(query, multiple)
../../../.local/lib/python3.5/site-packages/hrpc/object_proxy.py:92: in __call__
return self._client__.evaluate(self.__call_no_evaluate__(remote_obj_cache, *args))
../../../.local/lib/python3.5/site-packages/hrpc/client.py:63: in evaluate
self.transport.send({'id': reqid, 'uri': obj_proxy._uri__, 'method': obj_proxy._invocation_path__})
```

```
self =
req = {'id': '051d4de0-a238-4eaf-af08-a2e1d9523a76', 'method': (('getattr', 'selector'), ('getattr', 'select'), ('call', (('...', (...))), ('', False)))), 'session_id': '797fc382-a8b1-47a3-9440-c853748e7cb2', 'uri': 'poco-uiautomation-framework'}

def send(self, req):
req['session_id'] = self.session_id
try:
r = requests.post(self.endpoint, data=json.dumps(req), headers={'Content-Type': 'application/json'})
self.rpc_client.put_response(r.json())
except (ConnectionError, ValueError) as e:
> raise TransportDisconnected(e)
E hrpc.exceptions.TransportDisconnected: HTTPConnectionPool(host='127.0.0.1', port=15687): Max retries exceeded with url: / (Caused by NewConnectionError(': Failed to establish a new connection: [Errno 111] Connection refused',))
```

**To Reproduce**
Steps to reproduce the behaviour:
1. poco("***").exists()

**Expected behaviour**

**Screenshots**
none

**python version:** `python3.5`

**poco version:** `1.0.76`
> You can get poco version via `pip freeze` command.

**Smartphone (please complete the following information):**
- Device: [ZTE A2017][nubia NX563J]
- OS: [e.g. Android 7.1.1]
- more information if have

**Additional context**
Add any other context about the problem here.