Refactoring to eliminate duplicate DefaultTopology and DefaultTopologyGraph; eliminating a few fixmes.

Change-Id: Ie0e38dbf812bafdb7c94bba5278f0dd9af5be929
diff --git a/core/net/src/main/java/org/onosproject/net/topology/impl/DefaultTopologyProvider.java b/core/net/src/main/java/org/onosproject/net/topology/impl/DefaultTopologyProvider.java
index e9ab196..20a5ad3 100644
--- a/core/net/src/main/java/org/onosproject/net/topology/impl/DefaultTopologyProvider.java
+++ b/core/net/src/main/java/org/onosproject/net/topology/impl/DefaultTopologyProvider.java
@@ -279,8 +279,7 @@
             try {
                 buildTopology(reasons);
             } catch (Exception e) {
-                log.warn("Unable to compute topology due to: {}", e.getMessage());
-                log.debug("Unable to compute topology", e);
+                log.warn("Unable to compute topology", e);
             }
         }
     }