make secop.poller.Poller default

modules using the old poller (now called secop.poller.BasicPoller)
need to explcitly declare it (pollerClass = BasicPoller)

BasicPoller is still used in:

secop_mlz/amagnet.py
secop_mlz/entangle.py
secop/simulation.py

Remark: before removing BasicPoller we may need a replacement for
Readable.pollParams

Change-Id: If1ae8b68e02f13e601334656b818337c882e06cc
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21910
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/protocol/interface/tcp.py

@@ -122,8 +122,9 @@ class TCPRequestHandler(socketserver.BaseRequestHandler):
                 try:
                     msg = decode_msg(origin)
                 except Exception as err:
-                    # we have to decode 'origin' here. utf-8 and ascii may lead to encoding errors
-                    msg = origin.decode('latin-1').split(' ', 3)
+                    # we have to decode 'origin' here
+                    # use latin-1, as utf-8 or ascii may lead to encoding errors
+                    msg = origin.decode('latin-1').split(' ', 3) + (None,) # make sure len(msg) > 1
                     result = (ERRORPREFIX + msg[0], msg[1], ['InternalError', str(err),
                                                              {'exception': formatException(),
                                                               'traceback': formatExtendedStack()}])