Use time.sleep() instead of eventlet.sleep()

In a patched environment, time.sleep will be eventlet.sleep, so this
does not have any actual impact, but it removes one direct dependency on
eventlet.

Change-Id: I54112d061fa8118a9a6d91abf07442d8834425b5

cinderclient/client.py

@@ -25,6 +25,7 @@ import logging
 import os
 import pkgutil
 import re
+from time import sleep
 import urllib
 from urllib import parse as urlparse
 
@@ -42,10 +43,6 @@ from cinderclient import api_versions
 from cinderclient import exceptions
 import cinderclient.extension
 
-try:
-    from eventlet import sleep
-except ImportError:
-    from time import sleep
 
 try:
     osprofiler_web = importutils.try_import("osprofiler.web")