device config operator

Combination operator for device-related configuration information,
including tests.

Change-Id: I0320f7b568979063947a37cf2749daae7a1a05f1
diff --git a/incubator/api/src/main/java/org/onosproject/incubator/net/config/basics/BasicElementConfig.java b/incubator/api/src/main/java/org/onosproject/incubator/net/config/basics/BasicElementConfig.java
index 39f767a..1b13915 100644
--- a/incubator/api/src/main/java/org/onosproject/incubator/net/config/basics/BasicElementConfig.java
+++ b/incubator/api/src/main/java/org/onosproject/incubator/net/config/basics/BasicElementConfig.java
@@ -30,6 +30,8 @@
     public static final String RACK_ADDRESS = "rackAddress";
     public static final String OWNER = "owner";
 
+    protected static final double DEFAULT_COORD = -1.0;
+
     /**
      * Returns friendly label for the element.
      *
@@ -55,7 +57,7 @@
      * @return element latitude; -1 if not set
      */
     public double latitude() {
-        return get(LATITUDE, -1.0);
+        return get(LATITUDE, DEFAULT_COORD);
     }
 
     /**
@@ -74,7 +76,7 @@
      * @return element latitude; -1 if not set
      */
     public double longitude() {
-        return get(LONGITUDE, -1.0);
+        return get(LONGITUDE, DEFAULT_COORD);
     }
 
     /**