[ONOS-7114] Meter Subsystem Refactoring

Changes:
- Moves meter counters in the store
- Uses atomic counter map for meter counters
- Implements atomic counter map adapter and test atomic counter map
- Introduces free meter id
- Changes allocate meter id
- Implements unit tests for MeterManager and MeterStore

Change-Id: I45e3debc0e43ca7edcf6e3b4065866634f76f9f7
diff --git a/core/api/src/test/java/org/onosproject/store/service/AtomicCounterMapAdapter.java b/core/api/src/test/java/org/onosproject/store/service/AtomicCounterMapAdapter.java
new file mode 100644
index 0000000..df7d270
--- /dev/null
+++ b/core/api/src/test/java/org/onosproject/store/service/AtomicCounterMapAdapter.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2017-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.store.service;
+
+/**
+ * Testing adapter for the atomic counter map.
+ */
+public class AtomicCounterMapAdapter<K> implements AtomicCounterMap<K> {
+
+    @Override
+    public long incrementAndGet(K key) {
+        return 0;
+    }
+
+    @Override
+    public long decrementAndGet(K key) {
+        return 0;
+    }
+
+    @Override
+    public long getAndIncrement(K key) {
+        return 0;
+    }
+
+    @Override
+    public long getAndDecrement(K key) {
+        return 0;
+    }
+
+    @Override
+    public long addAndGet(K key, long delta) {
+        return 0;
+    }
+
+    @Override
+    public long getAndAdd(K key, long delta) {
+        return 0;
+    }
+
+    @Override
+    public long get(K key) {
+        return 0;
+    }
+
+    @Override
+    public long put(K key, long newValue) {
+        return 0;
+    }
+
+    @Override
+    public long putIfAbsent(K key, long newValue) {
+        return 0;
+    }
+
+    @Override
+    public boolean replace(K key, long expectedOldValue, long newValue) {
+        return false;
+    }
+
+    @Override
+    public long remove(K key) {
+        return 0;
+    }
+
+    @Override
+    public boolean remove(K key, long value) {
+        return false;
+    }
+
+    @Override
+    public int size() {
+        return 0;
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return false;
+    }
+
+    @Override
+    public void clear() {
+
+    }
+
+    @Override
+    public String name() {
+        return null;
+    }
+}