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/simulation.py

@@ -27,10 +27,12 @@ from time import sleep
 
 from secop.datatypes import FloatRange
 from secop.lib import mkthread
-from secop.modules import Drivable, Module, Parameter, Readable, Writable
+from secop.modules import Drivable, Module, Parameter, Readable, Writable, BasicPoller
 
 
 class SimBase:
+    pollerClass = BasicPoller
+
     def __init__(self, cfgdict):
         # spice up parameters if requested by extra property
         # hint: us a comma-separated list if mor than one extra_param
@@ -68,7 +70,7 @@ class SimBase:
         self.log.info('sim thread ended')
 
     def sim(self):
-        return True
+        return True # nothing to do, stop thread
 
     def read_value(self):
         if 'jitter' in self.accessibles:
@@ -138,6 +140,7 @@ class SimDrivable(SimBase, Drivable):
             except Exception:
                 pass
         self.status = self.Status.IDLE, ''
+        return False # keep thread running
 
     def _hw_wait(self):
         while self.status[0] == self.Status.BUSY: