add PolicyFixture for functional test.

At present, policy_data is empty.
And policy_data will be written in a policy.json file in /tmp path.
such as:
    /tmp/tmppgM04u/tmpgVJy4J/policy.json

So we want to pass the authorization for api test, we need to add the policy
item in this policy_data.

Such as:
 policy_data = """
 {
   'nimble:instance:get': '@'
 }
 """

Change-Id: I1a645312ea8ba98310945121c0205280ac740c09

nimble/tests/base.py

@@ -26,6 +26,7 @@ import testscenarios
 
 from nimble.common import config as nimble_config
 from nimble.common import context as nimble_context
+from nimble.tests import policy_fixture
 
 
 CONF = cfg.CONF
@@ -57,6 +58,7 @@ class TestCase(base.BaseTestCase):
             pecan.set_config({}, overwrite=True)
 
         self.addCleanup(reset_pecan)
+        self.policy = self.useFixture(policy_fixture.PolicyFixture())
 
     def _set_config(self):
         self.cfg_fixture = self.useFixture(config_fixture.Config(cfg.CONF))

nimble/tests/policy_fixture.py

@@ -0,0 +1,43 @@
+# Copyright 2016 Intel
+#
+# 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.
+
+import os
+
+import fixtures
+from oslo_config import cfg
+from oslo_policy import opts as policy_opts
+
+from nimble.common import policy as nimble_policy
+
+CONF = cfg.CONF
+
+policy_data = """
+{
+
+}
+"""
+
+
+class PolicyFixture(fixtures.Fixture):
+    def setUp(self):
+        super(PolicyFixture, self).setUp()
+        self.policy_dir = self.useFixture(fixtures.TempDir())
+        self.policy_file_name = os.path.join(self.policy_dir.path,
+                                             'policy.json')
+        with open(self.policy_file_name, 'w') as policy_file:
+            policy_file.write(policy_data)
+        policy_opts.set_defaults(CONF)
+        CONF.set_override('policy_file', self.policy_file_name, 'oslo_policy')
+        nimble_policy._ENFORCER = None
+        self.addCleanup(nimble_policy.get_enforcer().clear)