iam: use modern helper to allow sts

previous implementation ignored the session token when present

lib/ansible/modules/cloud/amazon/iam.py

@@ -576,13 +576,10 @@ def main():
         module.fail_json(changed=False, msg="iam_type: role, cannot currently be updated, "
                              "please specificy present or absent")
 
-    ec2_url, aws_access_key, aws_secret_key, region = get_ec2_creds(module)
+    region, ec2_url, aws_connect_kwargs = get_aws_connection_info(module)
 
     try:
-        iam = boto.iam.connection.IAMConnection(
+        iam = boto.iam.connection.IAMConnection(**aws_connect_kwargs)
-            aws_access_key_id=aws_access_key,
-            aws_secret_access_key=aws_secret_key,
-        )
     except boto.exception.NoAuthHandlerFound, e:
         module.fail_json(msg=str(e))