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>

secop/client/baseclient.py

@@ -44,7 +44,7 @@ from secop.protocol.messages import BUFFERREQUEST, COMMANDREQUEST, \
     READREQUEST, REQUEST2REPLY, WRITEREPLY, WRITEREQUEST
 
 
-class TCPConnection(object):
+class TCPConnection:
     # disguise a TCP connection as serial one
 
     def __init__(self, host, port):
@@ -136,7 +136,7 @@ class TCPConnection(object):
             self.writeline(line)
 
 
-class Value(object):
+class Value:
     t = None  # pylint: disable = C0103
     u = None
     e = None
@@ -165,7 +165,7 @@ class Value(object):
         return self.fmtstr % self.value
 
 
-class Client(object):
+class Client:
     secop_id = 'unknown'
     describing_data = {}
     stopflag = False
@@ -175,7 +175,7 @@ class Client(object):
         if 'testing' not in opts:
             self.log = mlzlog.log.getChild('client', True)
         else:
-            class logStub(object):
+            class logStub:
 
                 def info(self, *args):
                     pass