Implements policer-meter-mapping [ONOS-5867]

Changes
- Adds Policer config behavior and its implementation
- Implements id mapping
- Adds tests for OpenFlowPolicerConfig
- Adds free id api to MeterService and MeterStore
- Improves test for MeterStore

Change-Id: Ibb47375430e253131d9d9c8a60e61023ee6c8225
diff --git a/core/net/src/main/java/org/onosproject/net/meter/impl/MeterManager.java b/core/net/src/main/java/org/onosproject/net/meter/impl/MeterManager.java
index 2bd9746..5d7965b 100644
--- a/core/net/src/main/java/org/onosproject/net/meter/impl/MeterManager.java
+++ b/core/net/src/main/java/org/onosproject/net/meter/impl/MeterManager.java
@@ -243,11 +243,18 @@
         return store.getAllMeters();
     }
 
-    private MeterId allocateMeterId(DeviceId deviceId) {
+    @Override
+    public MeterId allocateMeterId(DeviceId deviceId) {
         // We delegate direclty to the store
         return store.allocateMeterId(deviceId);
     }
 
+    @Override
+    public void freeMeterId(DeviceId deviceId, MeterId meterId) {
+        // We delegate direclty to the store
+        store.freeMeterId(deviceId, meterId);
+    }
+
     private class InternalMeterProviderService
             extends AbstractProviderService<MeterProvider>
             implements MeterProviderService {