[SONA] OpenstackSwitching : network() and subnet()

- Added subnet information to OpenstackNetwork class
- Added a new interface, subnet() to return the subnet information.

Change-Id: Ib46455b297909275ba36659efaee2320a111a65e
diff --git a/apps/openstackswitching/api/src/main/java/org/onosproject/openstackswitching/OpenstackSwitchingService.java b/apps/openstackswitching/api/src/main/java/org/onosproject/openstackswitching/OpenstackSwitchingService.java
index be566f0..1ed4f6f 100644
--- a/apps/openstackswitching/api/src/main/java/org/onosproject/openstackswitching/OpenstackSwitchingService.java
+++ b/apps/openstackswitching/api/src/main/java/org/onosproject/openstackswitching/OpenstackSwitchingService.java
@@ -86,8 +86,16 @@
      * Returns network information list for the network ID given.
      *
      * @param networkId Network ID
-     * @return network information list
+     * @return network information list, or null if not present
      */
     OpenstackNetwork network(String networkId);
 
+
+    /**
+     * Returns subnet information for the subnet ID give.
+     *
+     * @param subnetId Subnet ID
+     * @return subnet information, or null if not present
+     */
+    OpenstackSubnet subnet(String subnetId);
 }