Simplify the validation of required fields of pipeline source

- The required field "meters" (or "counters") validation is invalid
- The validation of these required fields of SampleSource and EventSource
  are unnecessary

Change-Id: Ifda35d7ff0e5baa1a97017d9deb6db7613fb8e31

ceilometer/pipeline.py

@@ -293,11 +293,7 @@ class EventSource(Source):
 
     def __init__(self, cfg):
         super(EventSource, self).__init__(cfg)
-        try:
-            self.events = cfg['events']
-        except KeyError as err:
-            raise PipelineException(
-                "Required field %s not specified" % err.args[0], cfg)
+        self.events = cfg.get('events')
         self.check_source_filtering(self.events, 'events')
 
     def support_event(self, event_name):
@@ -315,13 +311,8 @@ class SampleSource(Source):
 
     def __init__(self, cfg):
         super(SampleSource, self).__init__(cfg)
-        try:
-            # 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)
-
+        # Support 'counters' for backward compatibility
+        self.meters = cfg.get('meters', cfg.get('counters'))
         try:
             self.interval = int(cfg.get('interval', 600))
         except ValueError:

ceilometer/tests/unit/test_decoupled_pipeline.py

@@ -103,6 +103,10 @@ class TestDecoupledPipeline(pipeline_base.BasePipelineTestCase):
         del self.pipeline_cfg['sinks']
         self._exception_create_pipelinemanager()
 
+    def test_source_no_meters_or_counters(self):
+        del self.pipeline_cfg['sources'][0]['counters']
+        self._exception_create_pipelinemanager()
+
     def test_source_dangling_sink(self):
         self.pipeline_cfg['sources'].append({
             'name': 'second_source',