further fixes of py3 issues

complaints by pylint are mainly related to
- remove object from base list in class definitions
- unnecessary else/elif after return/raise

Change-Id: I13d15449149cc8bba0562338d0c9c42e97163bdf
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21325
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_client_baseclient.py

@@ -30,7 +30,7 @@ from secop.client.baseclient import Client
 # define Test-only connection object
 
 
-class TestConnect(object):
+class TestConnect:
     callbacks = []
 
     def writeline(self, line):