Some tests fail sometimes, because of plugin loading exception

watcher.tests.decision_engine.loading.test_default_planner_loader.TestDefaultPlannerLoader.test_endpoints
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Captured traceback:
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    Traceback (most recent call last):
      File "watcher/tests/decision_engine/loading/test_default_planner_loader.py", line 29, in test_endpoints
        loaded = self.loader.load(endpoint)
      File "watcher/common/loader/default.py", line 59, in load
        raise exception.LoadingError(name=name)
    watcher.common.exception.LoadingError: Error loading plugin 'default'

watcher.tests.decision_engine.loading.test_collector_loader.TestLoadClusterDataModelCollectors.test_load_cluster_data_model_collectors(compute)
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Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):
      File "/data/bcom/OPENSTACK/watcher/.tox/py27/local/lib/python2.7/site-packages/mock/mock.py", line 1305, in patched
        return func(*args, **keywargs)
      File "watcher/tests/decision_engine/loading/test_collector_loader.py", line 82, in test_load_cluster_data_model_collectors
        collector = self.collector_loader.load(self.collector_name)
      File "watcher/common/loader/default.py", line 59, in load
        raise exception.LoadingError(name=name)
    watcher.common.exception.LoadingError: Error loading plugin 'compute'