various fixes

- nodestatechange callback must appear after the online attribute
  is changed
- IntRange: move range validation outside of try except
- fixes on some error names
- well defined error message 'no such class' in secop.lib.get_class
- try again 4 times when starting Tcp Server on EADDRINUSE
- fix error handling

Change-Id: I4eee9b79ea8173936b9f5193b87e006ac8fca827
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/26171
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/server.py

@@ -256,7 +256,7 @@ class Server:
                     self.modules[modname] = modobj
                 except ConfigError as e:
                     errors.append('error creating module %s:' % modname)
-                    for errtxt in e.args[0]:
+                    for errtxt in e.args[0] if isinstance(e.args[0], list) else [e.args[0]]:
                         errors.append('  ' + errtxt)
                 except Exception:
                     failure_traceback = traceback.format_exc()