Port exhaustion

[dave4you]

Current implementation causes port exhaustion. This can be solved implementing urllib3 PoolManager. Implementing this prevents opening a new port for every http request. This means less processor overhead and 30% time winst.

#Add
from urllib3 import PoolManager

class SubstrateInterface:

    def __init__

                #Add 
                self.http = PoolManager()


    def rpc_request(self, method, params):

                else:

#previous: response = requests.request("POST", self.url, data=json.dumps(payload), headers=self.default_headers)
response = self.http.request("POST", self.url, body=json.dumps(payload), headers=self.default_headers)

#previous: if response.status_code != 200:
if response.status != 200:
                              #previous: raise SubstrateRequestException("RPC request failed with HTTP status code {}".format(response.status_code ))
raise SubstrateRequestException("RPC request failed with HTTP status code {}".format(response.status))

#previous: json_body = response.json()
json_body = json.loads(response.data.decode('utf-8'))`