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/lib/__init__.py

@@ -32,6 +32,7 @@ import subprocess
 import sys
 import threading
 import traceback
+import importlib
 from os import path
 
 repodir = path.abspath(path.join(path.dirname(__file__), '..', '..'))
@@ -51,7 +52,7 @@ CONFIG = {
 
 unset_value = object()
 
-class lazy_property(object):
+class lazy_property:
     """A property that calculates its value only once."""
 
     def __init__(self, func):
@@ -89,7 +90,6 @@ def clamp(_min, value, _max):
 def get_class(spec):
     """loads a class given by string in dotted notaion (as python would do)"""
     modname, classname = spec.rsplit('.', 1)
-    import importlib
     if modname.startswith('secop'):
         module = importlib.import_module(modname)
     else: