Implement watcher datamodel list in watcher-api

1. Add datamodel api and policy_enfoce file.
2. Add related unittest for data_model api and policy.

Partially Implements:blueprint show-datamodel-api

Change-Id: I1654685d8cf04db5dd132d43a8640ddf91893cad

watcher/common/policies/data_model.py

@@ -0,0 +1,37 @@
+# Copyright 2019 ZTE Corporation.
+#
+#    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.
+
+from oslo_policy import policy
+
+from watcher.common.policies import base
+
+DATA_MODEL = 'data_model:%s'
+
+rules = [
+    policy.DocumentedRuleDefault(
+        name=DATA_MODEL % 'get_all',
+        check_str=base.RULE_ADMIN_API,
+        description='List data model.',
+        operations=[
+            {
+                'path': '/v1/data_model',
+                'method': 'GET'
+            }
+        ]
+    ),
+]
+
+
+def list_rules():
+    return rules