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/proxy.py

@@ -144,10 +144,12 @@ class SecNode(Module):
     uri = Property('uri of a SEC node', datatype=StringType())
 
     def earlyInit(self):
+        super().earlyInit()
         self.secnode = SecopClient(self.uri, self.log)
 
-    def startModule(self, started_callback):
-        self.secnode.spawn_connect(started_callback)
+    def startModule(self, start_events):
+        super().startModule(start_events)
+        self.secnode.spawn_connect(start_events.get_trigger())
 
     @Command(StringType(), result=StringType())
     def request(self, msg):