Support custom requests session in presto connections (#106)

* add connection options to presto

* requests_session

* format

* doc

* address comments

omniduct/databases/presto.py

@@ -49,21 +49,25 @@ def NAMESPACE_DEFAULT(self):
         }
 
     @override
-    def _init(self, catalog='default', schema='default', server_protocol='http', source=None):
+    def _init(self, catalog='default', schema='default', server_protocol='http', source=None, requests_session=None):
         """
         catalog (str): The default catalog to use in database queries.
         schema (str): The default schema/database to use in database queries.
         server_protocol (str): The protocol over which to connect to the Presto REST
             service ('http' or 'https'). (default='http')
         source (str): The source of this query (by default "omniduct <version>").
             If manually specified, result will be: "<source> / omniduct <version>".
+        requests_session (requests.Session): an optional requests.Session object for advanced usage.
+            Passed through to the pyhive Cursor which supports custom requests sessions for advanced usage
+            such as custom headers, cookie values, retry logic, etc.
         """
         self.catalog = catalog
         self.schema = schema
         self.server_protocol = server_protocol
         self.source = source
         self.__presto = None
         self.connection_fields += ('catalog', 'schema')
+        self._requests_session = requests_session
 
     @property
     def source(self):
@@ -115,7 +119,8 @@ def _execute(self, statement, cursor, wait, session_properties):
             cursor = cursor or presto.Cursor(
                 host=self.host, port=self.port, username=self.username, password=self.password,
                 catalog=self.catalog, schema=self.schema, session_props=session_properties,
-                poll_interval=1, source=self.source, protocol=self.server_protocol
+                poll_interval=1, source=self.source, protocol=self.server_protocol,
+                requests_session=self._requests_session
             )
             cursor.execute(statement)
             status = cursor.poll()