Enable checkstyle trailing spaces rule

Enable the checkstyle rule that detects unneeded trailing spaces
and fix the violations of the rule.

Change-Id: I65567c87142c5a257f0230a55bc4376e770d416f
diff --git a/src/main/java/net/onrc/onos/apps/bgproute/Ptree.java b/src/main/java/net/onrc/onos/apps/bgproute/Ptree.java
index b34364b..f85c49c 100644
--- a/src/main/java/net/onrc/onos/apps/bgproute/Ptree.java
+++ b/src/main/java/net/onrc/onos/apps/bgproute/Ptree.java
@@ -7,7 +7,7 @@
  * the Ptree as they contain data fundamental to the structure of the tree.
  * You should put RIB entries in and get RIB entries out.
  * Also we need to get rid of the referencing scheme to determine when to delete nodes.
- * Deletes should be explicit, and there's no need to keep track of references if 
+ * Deletes should be explicit, and there's no need to keep track of references if
  * we don't leak them out the the Ptree.
  */
 public class Ptree {