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/lib/asynconn.py

@@ -159,14 +159,20 @@ class AsynTcp(AsynConn):
         return b''.join(data)
 
     def recv(self):
-        """return bytes received within 1 sec"""
+        """return bytes in the recv buffer
+
+        or bytes received within 1 sec
+        """
         try:
             data = self.connection.recv(8192)
             if data:
                 return data
-        except socket.timeout:
+        except (socket.timeout, TimeoutError):
             # timeout while waiting
             return b''
+        # note that when no data is sent on a connection, an interruption might
+        # not be detected within a reasonable time. sending a heartbeat should
+        # help in this case.
         raise ConnectionClosed()  # marks end of connection