Change pipeline_manager to instance attribute in hooks

We should not assume the type of object which pecan.make_app() return
because it varies based on different configuration settings during the
test.

In order to achieve this, we have to change the PipelineHook's class
attribute pipeline_manager to be instance attribute, otherwise,
different api server created for different DB back-end would end up
sharing the same pipeline_manager which would break test tests.

(Failing unit tests in gate, manually booting it out. Please *DONT*
run recheck no bug on unit test failures).

Change-Id: Ic4370b1b8bec5723a0d719c74bdcdad8a6552912
Closes-Bug: #1327032

ceilometer/api/hooks.py

@@ -48,13 +48,10 @@ class PipelineHook(hooks.PecanHook):
     new samples can be posted via the /v2/meters/ API.
     '''
 
-    pipeline_manager = None
-
     def __init__(self):
-        if self.__class__.pipeline_manager is None:
-            # this is done here as the cfg options are not available
-            # when the file is imported.
-            self.__class__.pipeline_manager = pipeline.setup_pipeline()
+        # this is done here as the cfg options are not available
+        # when the file is imported.
+        self.pipeline_manager = pipeline.setup_pipeline()
 
     def before(self, state):
         state.request.pipeline_manager = self.pipeline_manager

ceilometer/tests/api/v2/test_post_samples_scenarios.py

@@ -36,25 +36,19 @@ class TestPostSamples(FunctionalTest,
             del m['message_signature']
         self.published.append(data)
 
-    def patch_publishers(self):
+    def fake_get_rpc_client(self, **kwargs):
         cast_ctxt = mock.Mock()
         cast_ctxt.cast.side_effect = self.fake_cast
-        found = False
-        pipeline_hook = self.app.app.application.app.hooks[2]
-        for pipeline in pipeline_hook.pipeline_manager.pipelines:
-            for publisher in pipeline.publishers:
-                if hasattr(publisher, 'rpc_client'):
-                    self.useFixture(mockpatch.PatchObject(
-                        publisher.rpc_client, 'prepare',
-                        return_value=cast_ctxt))
-                    found = True
-        if not found:
-            raise Exception('fail to patch the rpc publisher')
+        client = mock.Mock()
+        client.prepare.return_value = cast_ctxt
+        return client
 
     def setUp(self):
-        super(TestPostSamples, self).setUp()
         self.published = []
-        self.patch_publishers()
+        self.useFixture(mockpatch.Patch(
+                        'ceilometer.messaging.get_rpc_client',
+                        new=self.fake_get_rpc_client))
+        super(TestPostSamples, self).setUp()
 
     def test_one(self):
         s1 = [{'counter_name': 'apples',