fix: do not create redundant session in session token manager

Author: eiri

ibmcloudant/couchdb_session_token_manager.py

@@ -54,7 +54,7 @@ def __init__(self, username: str, password: str,
 
         self.token = None
 
-        self.http_client = Session()
+        self.http_client = None
         self.http_config = {}
         self.jar = None
         self.headers = None
@@ -67,6 +67,9 @@ def request_token(self):
              A CookieJar of Cookies the server sent back.
         """
 
+        if not isinstance(self.http_client, Session):
+            raise TypeError("http_client parameter must be a requests.sessions.Session")
+
         response = self.http_client.request(
             method='POST',
             url=self.url + "/_session",