fix and improved Attached

- Attached checks now for proper base class
- fixes an error in Attached: attached saved in attachedModules
  dict instead on the Attached object (which sits on the class!)
+ fix: in testonly mode errors must be logged before returning
+ fix: use repr of exception in poll to check for repeated errors

Change-Id: I141fa107fed48e58b55ddf1e071987656c0f618f
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27913
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_attach.py

@@ -75,4 +75,6 @@ def test_attach():
     assert m.propertyValues['att'] == 'a'
     srv.dispatcher.register_module(a, 'a')
     srv.dispatcher.register_module(m, 'm')
+    assert m.att == 'a'
+    m.attachedModules = {'att': a}
     assert m.att == a