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/incubator/store/src/main/java/org/onosproject/incubator/store/meter/impl/DistributedMeterStore.java b/incubator/store/src/main/java/org/onosproject/incubator/store/meter/impl/DistributedMeterStore.java
index cf4bfcb..28cc7ba 100644
--- a/incubator/store/src/main/java/org/onosproject/incubator/store/meter/impl/DistributedMeterStore.java
+++ b/incubator/store/src/main/java/org/onosproject/incubator/store/meter/impl/DistributedMeterStore.java
@@ -433,6 +433,10 @@
 
     @Override
     public void freeMeterId(DeviceId deviceId, MeterId meterId) {
+        // Avoid to free meter not allocated
+        if (meterIdGenerators.get(deviceId) < meterId.id()) {
+            return;
+        }
         // Update the availability
         updateMeterIdAvailability(deviceId, meterId, true);
     }