Make interval optional in pipeline

Make interval in pipeline yaml file optional. If interval is not
provided, a default value should be given.

Change-Id: I557e66902c272331bd1e2c72d03d495f0924d573
Closes-Bug: #1423957

ceilometer/pipeline.py

@@ -278,15 +278,16 @@ class SampleSource(Source):
     def __init__(self, cfg):
         super(SampleSource, self).__init__(cfg)
         try:
-            try:
-                self.interval = int(cfg['interval'])
-            except ValueError:
-                raise PipelineException("Invalid interval value", cfg)
             # Support 'counters' for backward compatibility
             self.meters = cfg.get('meters', cfg.get('counters'))
         except KeyError as err:
             raise PipelineException(
                 "Required field %s not specified" % err.args[0], cfg)
+
+        try:
+            self.interval = int(cfg.get('interval', 600))
+        except ValueError:
+            raise PipelineException("Invalid interval value", cfg)
         if self.interval <= 0:
             raise PipelineException("Interval value should > 0", cfg)
 

ceilometer/tests/pipeline_base.py

@@ -210,7 +210,11 @@ class BasePipelineTestCase(base.BaseTestCase):
 
     def test_no_interval(self):
         self._unset_pipeline_cfg('interval')
-        self._exception_create_pipelinemanager()
+        pipeline_manager = pipeline.PipelineManager(self.pipeline_cfg,
+                                                    self.transformer_manager)
+
+        pipe = pipeline_manager.pipelines[0]
+        self.assertEqual(600, pipe.get_interval())
 
     def test_no_publishers(self):
         self._unset_pipeline_cfg('publishers')