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_mlz/entangle.py

@@ -41,7 +41,7 @@ from secop.errors import CommunicationFailedError, \
     ConfigError, HardwareError, ProgrammingError
 from secop.lib import lazy_property
 from secop.modules import Command, Drivable, \
-    Module, Override, Parameter, Readable
+    Module, Override, Parameter, Readable, BasicPoller
 
 #####
 
@@ -158,6 +158,8 @@ class PyTangoDevice(Module):
     execution and attribute operations with logging and exception mapping.
     """
 
+    pollerClass = BasicPoller
+
     parameters = {
         'comtries': Parameter('Maximum retries for communication',
                           datatype=IntRange(1, 100), default=3, readonly=False,