Add checks on host connectivity

[davinerd]

$ python3 brute.py dump --url http://localhost:3000/graphql
Traceback (most recent call last):
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/connection.py", line 159, in _new_conn
    conn = connection.create_connection(
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/util/connection.py", line 84, in create_connection
    raise err
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/util/connection.py", line 74, in create_connection
    sock.connect(sa)
ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/connectionpool.py", line 670, in urlopen
    httplib_response = self._make_request(
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/connectionpool.py", line 392, in _make_request
    conn.request(method, url, **httplib_request_kw)
  File "/usr/lib/python3.8/http/client.py", line 1255, in request
    self._send_request(method, url, body, headers, encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1301, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1250, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.8/http/client.py", line 1010, in _send_output
    self.send(msg)
  File "/usr/lib/python3.8/http/client.py", line 950, in send
    self.connect()
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/connection.py", line 187, in connect
    conn = self._new_conn()
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/connection.py", line 171, in _new_conn
    raise NewConnectionError(
urllib3.exceptions.NewConnectionError: <urllib3.connection.HTTPConnection object at 0x7f727e06a940>: Failed to establish a new connection: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/requests/adapters.py", line 439, in send
    resp = conn.urlopen(
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/connectionpool.py", line 726, in urlopen
    retries = retries.increment(
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/urllib3/util/retry.py", line 446, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='localhost', port=3000): Max retries exceeded with url: /graphql (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f727e06a940>: Failed to establish a new connection: [Errno 111] Connection refused'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "brute.py", line 53, in <module>
    plugin.attack()
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/plugins/dump/dump.py", line 25, in attack
    f = requests.post(self.GQL_ENDPOINT, headers=utils.set_request_headers(), json={"query": self.introspection_query})
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/requests/api.py", line 119, in post
    return request('post', url, data=data, json=json, **kwargs)
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/requests/api.py", line 61, in request
    return session.request(method=method, url=url, **kwargs)
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/requests/sessions.py", line 530, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/requests/sessions.py", line 643, in send
    r = adapter.send(request, **kwargs)
  File "/home/dab/codes/mycodes/github_repos/gql_intruder/venv/lib/python3.8/site-packages/requests/adapters.py", line 516, in send
    raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPConnectionPool(host='localhost', port=3000): Max retries exceeded with url: /graphql (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f727e06a940>: Failed to establish a new connection: [Errno 111] Connection refused'))