Gracefully handle duplicate delete requests.

This code change is to handle any gracefully handle duplicate delete requests
sent by external entities, in this case service monitor.
This code change will log and handle the key not found excpetion and proceed.

The service monitor, sending  duplicate deletes is tracked by bug: 1636932

Change-Id: I606561ca0e3c570713b41c196325180a16f96987
closes-bug: #1635901

src/config/api-server/vnc_cfg_ifmap.py

@@ -633,13 +633,24 @@ def _delete_id_self_meta(self, self_imid, meta_name):
                                       True)
         self._publish_to_ifmap_enqueue('delete', del_str)
 
-        # del meta from cache and del id if this was last meta
-        if meta_name:
-            del self._id_to_metas[self_imid][meta_name]
-            if not self._id_to_metas[self_imid]:
+        try:
+
+            # del meta from cache and del id if this was last meta
+            if meta_name:
+                del self._id_to_metas[self_imid][meta_name]
+                if not self._id_to_metas[self_imid]:
+                    del self._id_to_metas[self_imid]
+            else:
                 del self._id_to_metas[self_imid]
-        else:
-            del self._id_to_metas[self_imid]
+
+        except KeyError:
+            # Case of delete received for an id which we do not know about.
+            # Could be a case of duplicate delete.
+            # There is nothing for us to do here. Just log and proceed.
+            msg = "Delete received for unknown imid(%s) meta_name(%s)." % \
+                  (self_imid, meta_name)
+            self.config_log(msg, level=SandeshLevel.SYS_DEBUG)
+
     # end _delete_id_self_meta
 
     def _delete_id_pair_meta_list(self, id1, meta_list):