Suppress exception stack traces on warning conditions to prevent STC faiures for non-fatal situations

Change-Id: I10d4945e92b3674f00725597d00fc13cc140c943
diff --git a/core/net/src/main/java/org/onosproject/net/packet/impl/PacketManager.java b/core/net/src/main/java/org/onosproject/net/packet/impl/PacketManager.java
index 98d1b41..b9ac1a4 100644
--- a/core/net/src/main/java/org/onosproject/net/packet/impl/PacketManager.java
+++ b/core/net/src/main/java/org/onosproject/net/packet/impl/PacketManager.java
@@ -498,7 +498,7 @@
                     }
                     pushRulesToDevice(device);
                 } catch (Exception e) {
-                    log.warn("Failed to process {}", event, e);
+                    log.warn("Failed to process {}: {}", event, e.getMessage());
                 }
             });
         }