Move a debug logging line by one

If, for some reason, the function name that comes in does not have a :,
which should never happen, we won't see the bogus line in the log
because we split it before we log it.

This seriously doesn't matter - we don't register functions without :'s
in them. But my eyes just can't stop staring at it.

Change-Id: I089ec1969b28367078ce969bfbfc5272f70318e6
diff --git a/zuul/rpclistener.py b/zuul/rpclistener.py
index d54da9f..5329c41 100644
--- a/zuul/rpclistener.py
+++ b/zuul/rpclistener.py
@@ -66,8 +66,8 @@
         while self._running:
             try:
                 job = self.worker.getJob()
-                z, jobname = job.name.split(':')
                 self.log.debug("Received job %s" % job.name)
+                z, jobname = job.name.split(':')
                 attrname = 'handle_' + jobname
                 if hasattr(self, attrname):
                     f = getattr(self, attrname)