Fix H405 violations and re-enable gating

H405 is a new rule in hacking 0.9, so fix new violations and
re-enable gating.

Change-Id: I61541fa0a9dc18ad938df54d56c65c972b151622

ceilometer/compute/notifications/cpu.py

@@ -28,8 +28,7 @@ LOG = log.getLogger(__name__)
 
 
 class ComputeMetricsNotificationBase(notifications.ComputeNotificationBase):
-    """Convert compute.metrics.update notifications into Samples
-    """
+    """Convert compute.metrics.update notifications into Samples."""
     event_types = ['compute.metrics.update']
     metric = None
     sample_type = None