Fix error module usage
Fix error module usage

Failures of gate-ceilometer-dsvm-tempest-plugin in some patchs occur:

Traceback (most recent call last):
  File "tempest/test.py", line 99, in wrapper
    return f(self, *func_args, **func_kwargs)
  File "/opt/stack/new/ceilometer/ceilometer/tests/tempest/api/test_telemetry_notification_api.py", line 52, in test_check_glance_v2_notifications
    self.await_samples(metric, query)
  File "/opt/stack/new/ceilometer/ceilometer/tests/tempest/api/base.py", line 131, in await_samples
    raise exceptions.TimeoutException(
AttributeError: 'module' object has no attribute 'TimeoutException'

It is caused by the inappropriate usage of exceptions module. Let's fix it.

Change-Id: I66ea550ce4255ca6b0a645a119faac0021fb2041

openstack/ceilometer,openstack/ceilometer