Enable checkstyle Javadoc Comment Style rule

Turn on the Javadoc Comment Style rule and fix
any violations that come up.  This is related to
requiring javadoc description comments to end
with a '.'

Change-Id: I19cf1b9f00d3040987e0b4c8b39461e2e0ad66b5
diff --git a/src/main/java/net/onrc/onos/core/util/PerformanceMonitor.java b/src/main/java/net/onrc/onos/core/util/PerformanceMonitor.java
index 0fb064e..389453f 100644
--- a/src/main/java/net/onrc/onos/core/util/PerformanceMonitor.java
+++ b/src/main/java/net/onrc/onos/core/util/PerformanceMonitor.java
@@ -9,7 +9,7 @@
 import org.slf4j.LoggerFactory;
 
 /**
- * Class for collecting performance measurements
+ * Class for collecting performance measurements.
  */
 public class PerformanceMonitor {
     private static final Logger log = LoggerFactory.getLogger(PerformanceMonitor.class);
@@ -36,7 +36,7 @@
     private static final double NORMALIZATION = Math.pow(10, 6);
 
     /**
-     * Start a performance measurement, identified by a tag
+     * Start a performance measurement, identified by a tag.
      * <p/>
      * Note: Only a single measurement can use the same tag at a time.
      * ..... not true anymore.
@@ -96,7 +96,7 @@
     }
 
     /**
-     * Write all performance measurements to the log
+     * Write all performance measurements to the log.
      */
     public void reportAll() {
         StringBuilder result = new StringBuilder();
@@ -149,7 +149,7 @@
     }
 
     /**
-     * Write the performance measurement for a tag to the log
+     * Write the performance measurement for a tag to the log.
      *
      * @param tag the tag name.
      */
@@ -169,14 +169,14 @@
     }
 
     /**
-     * A single performance measurement
+     * A single performance measurement.
      */
     public static class Measurement {
         long start;
         long stop = -1;
 
         /**
-         * Start the measurement
+         * Start the measurement.
          */
         public void start() {
             if (start <= 0) {
@@ -185,7 +185,7 @@
         }
 
         /**
-         * Stop the measurement
+         * Stop the measurement.
          */
         public void stop() {
             long now = System.nanoTime();
@@ -193,7 +193,7 @@
         }
 
         /**
-         * Stop the measurement at a specific time
+         * Stop the measurement at a specific time.
          *
          * @param time to stop
          */
@@ -204,7 +204,7 @@
         }
 
         /**
-         * Compute the elapsed time of the measurement in nanoseconds
+         * Compute the elapsed time of the measurement in nanoseconds.
          *
          * @return the measurement time in nanoseconds, or -1 if the measurement is stil running.
          */