server: service discovery over UDP.

implement RFC-005
- server broadcasts once on startup and answers to broadcasts
- small tool for listening on the port and sending broadcasts

Change-Id: I02d1184d6be62bef6f964eb9d238220aef062e94
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/34851
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Georg Brandl <g.brandl@fz-juelich.de>

frappy/secnode.py

@@ -54,8 +54,17 @@ class SecNode:
         self.name = name
 
     def add_secnode_property(self, prop, value):
+        """Add SECNode property. If starting with an underscore, it is exported
+        in the description."""
         self.nodeprops[prop] = value
 
+    def get_secnode_property(self, prop):
+        """Get SECNode property.
+
+        Returns None if not present.
+        """
+        return self.nodeprops.get(prop)
+
     def get_module(self, modulename):
         """ Returns a fully initialized module. Or None, if something went
         wrong during instatiating/initializing the module."""