server: Add early escapes to simplify logic

Add a couple early escapes to the bus_handler method.

Tested: Manually verified mapper content is the same after service
  discovery.
Change-Id: I9c0e08022176345797fd74809770ddfdfeffe904
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/obmc/mapper/server.py b/obmc/mapper/server.py
index e1f3af2..11e93ed 100644
--- a/obmc/mapper/server.py
+++ b/obmc/mapper/server.py
@@ -394,13 +394,13 @@
                 path, owner, old=old, new=[])
 
     def bus_handler(self, owned_name, old, new):
-        valid = False
-        if not obmc.dbuslib.bindings.is_unique(owned_name):
-            valid = self.bus_normalize(owned_name)
+        if obmc.dbuslib.bindings.is_unique(owned_name) or \
+                owned_name == obmc.mapper.MAPPER_NAME:
+            return
 
-        if valid and new:
+        if new:
             self.process_new_owner(owned_name, new)
-        if valid and old:
+        if old:
             # discard any unhandled signals
             # or in progress discovery
             if old in self.defer_signals: