Only warn about deprecation warnings once

Instead of repeatly emitting data about which
modules are deprecated again and again just warn
about those deprecation once and then never warn
about them again.

This is a good thing to have, and will be needed
as taskflow moves one of its classes used in cinder
to a new and longer-term location and will emit
deprecation about the usage of the old location.

Change-Id: I962f9bab920a03eca235c9e4591d367687e44954

bin/cinder-all

@@ -32,6 +32,9 @@ eventlet.monkey_patch()
 
 import os
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 from oslo.config import cfg
 

bin/cinder-api

@@ -22,6 +22,9 @@ eventlet.monkey_patch()
 
 import os
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 from oslo.config import cfg
 

bin/cinder-backup

@@ -20,6 +20,9 @@
 
 import os
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 import eventlet
 

bin/cinder-clear-rabbit-queues

@@ -23,6 +23,9 @@
 
 import os
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 from oslo.config import cfg
 

bin/cinder-manage

@@ -57,6 +57,9 @@ from __future__ import print_function
 
 import os
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 from oslo.config import cfg
 from oslo import messaging

bin/cinder-rpc-zmq-receiver

@@ -19,6 +19,9 @@ eventlet.monkey_patch()
 import contextlib
 import os
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 # If ../cinder/__init__.py exists, add ../ to Python search path, so that
 # it will override what happens to be installed in /usr/(local/)lib/python...

bin/cinder-scheduler

@@ -24,6 +24,9 @@ eventlet.monkey_patch()
 
 import os
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 from oslo.config import cfg
 

bin/cinder-volume

@@ -28,6 +28,9 @@ else:
     eventlet.monkey_patch()
 
 import sys
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 from oslo.config import cfg
 

bin/cinder-volume-usage-audit

@@ -38,6 +38,9 @@ from datetime import datetime
 import os
 import sys
 import traceback
+import warnings
+
+warnings.simplefilter('once', DeprecationWarning)
 
 from oslo.config import cfg