improve handling of module init methods

- complain when super call is omitted (this is a common programming
  error in Mixins)
- redesign waiting mechanism for startup

+ rename MultiEvent method 'setfunc' to 'get_trigger'

Change-Id: Ica27a75597321f2571a604a7a55448cffb1bec5e
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27369
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/lib/multievent.py

@@ -110,7 +110,7 @@ class MultiEvent(threading.Event):
     def waiting_for(self):
         return set(event.name for event in self.events)
 
-    def setfunc(self, timeout=None, name=None):
+    def get_trigger(self, timeout=None, name=None):
         """create a new single event and return its set method
 
         as a convenience method