improve error handling on client connections

- send a heartbeat, if no events for 5 sec.
  an interrupted connection (not closed by the other end) may
  not be detected for a long time when nothing is sent
+ make the error reply on a non SECoPEror more verbose
  e.g. "KeyError('foo')" instead of just "foo"
+ allow cfg file without nodeinterface
+ shorter logger name in HasIodev

Change-Id: I6b1ff23f9bf8c96feb25af44935596437b7d726f
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/23098
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/protocol/interface/tcp.py

@@ -145,7 +145,7 @@ class TCPRequestHandler(socketserver.BaseRequestHandler):
                                                                   'traceback': formatExtendedStack()}])
                     except Exception as err:
                         # create Error Obj instead
-                        result = (ERRORPREFIX + msg[0], msg[1], ['InternalError', str(err),
+                        result = (ERRORPREFIX + msg[0], msg[1], ['InternalError', repr(err),
                                                                  {'exception': formatException(),
                                                                   'traceback': formatExtendedStack()}])
                         print('--------------------')