Enable checkstyle rule to check for boolean simplifications

Enable the checkstyle "SimplifyBooleanExpression" rule and
fix any violations it reports.

Change-Id: If8a0226829da3339b9209324a8ea36a28f2138c4
diff --git a/src/main/java/net/onrc/onos/apps/forwarding/Forwarding.java b/src/main/java/net/onrc/onos/apps/forwarding/Forwarding.java
index 77703e5..08a68b6 100644
--- a/src/main/java/net/onrc/onos/apps/forwarding/Forwarding.java
+++ b/src/main/java/net/onrc/onos/apps/forwarding/Forwarding.java
@@ -386,7 +386,7 @@
                         }
                     }
 
-                    if (isflowEntryForThisSwitch == false) {
+                    if (!isflowEntryForThisSwitch) {
                         // If we don't find a flow entry for that switch, then we're
                         // in the middle of a rerouting (or something's gone wrong).
                         // This packet will be dropped as a victim of the rerouting.