Improve the method to loading configurations from OSGI

To avoid null value error, Use Tools.get() in org.onlab.util.Tools to load configs safely.

Refer to https://wiki.onosproject.org/display/ONOS/Component+Configuration

Change-Id: Ic8ab5bd41d1e374a0abb3c78e94c28df7854b85d
diff --git a/apps/fwd/src/main/java/org/onosproject/fwd/ReactiveForwarding.java b/apps/fwd/src/main/java/org/onosproject/fwd/ReactiveForwarding.java
index bb29e65..6653c63 100644
--- a/apps/fwd/src/main/java/org/onosproject/fwd/ReactiveForwarding.java
+++ b/apps/fwd/src/main/java/org/onosproject/fwd/ReactiveForwarding.java
@@ -35,6 +35,7 @@
 import org.onlab.packet.TpPort;
 import org.onlab.packet.UDP;
 import org.onlab.packet.VlanId;
+import org.onlab.util.Tools;
 import org.onosproject.cfg.ComponentConfigService;
 import org.onosproject.core.ApplicationId;
 import org.onosproject.core.CoreService;
@@ -372,8 +373,8 @@
                                               String propertyName) {
         Integer value = null;
         try {
-            String s = (String) properties.get(propertyName);
-            value = isNullOrEmpty(s) ? value : Integer.parseInt(s.trim());
+            String s = Tools.get(properties, propertyName);
+            value = isNullOrEmpty(s) ? value : Integer.parseInt(s);
         } catch (NumberFormatException | ClassCastException e) {
             value = null;
         }
@@ -391,10 +392,8 @@
                                              String propertyName) {
         boolean enabled = false;
         try {
-            String flag = (String) properties.get(propertyName);
-            if (flag != null) {
-                enabled = flag.trim().equals("true");
-            }
+            String flag = Tools.get(properties, propertyName);
+            enabled = isNullOrEmpty(flag) ? enabled : flag.equals("true");
         } catch (ClassCastException e) {
             // No propertyName defined.
             enabled = false;