MAINTENANCE: Python3 Avahi service publishing compatibility

In machinekit#324 it became obvious, that changes in how strings are represented in Python 3 from legacy Python 2 caused that request through DBus to Avahi were rejected. Python Avahi module includes function 'string_array_to_txt_array', which transcodes Python strings into byte arrays.

Only used on the TXT value, as all others seem to be working. (Minimal changes to just get working system.)

lib/python/machinekit/service.py

@@ -47,7 +47,8 @@ def publish(self):
 
         # insert fqdn in announcement
         fqdn = str(server.GetHostNameFqdn())
-        text = [t % {'fqdn': fqdn} for t in self.text]
+        text = avahi.string_array_to_txt_array(
+            [t % {'fqdn': fqdn} for t in self.text])
         name = self.name % {'fqdn': fqdn}
 
         iface = avahi.IF_UNSPEC
@@ -114,7 +115,8 @@ def __init__(
 
         if name is None:
             pid = os.getpid()
-            self.name = '%s service on %s pid %i' % (self.type.title(), self.host, pid)
+            self.name = '%s service on %s pid %i' % (
+                self.type.title(), self.host, pid)
 
         me = uuid.uuid1()
         self.status_txtrec = [