Centralize cooperative yield

Replace the remaining time.sleep calls use to trigger eventlet yield
to the existing nova.utils.cooperative_yield() call. This will help
us to disable such yielding in when the service is running in threading
mode and eventually drop the whole thing when nova removes eventlet.

Change-Id: I6b3fcba13f4d1c41d1fac2efe3cb4a943e66f8bb
Signed-off-by: Balazs Gibizer <gibi@redhat.com>

nova/scheduler/host_manager.py

@@ -19,7 +19,6 @@ Manage hosts in the current zone.
 
 import collections
 import functools
-import time
 
 import iso8601
 from oslo_log import log as logging
@@ -465,8 +464,7 @@ class HostManager(object):
                                                          "updated": False}
                         inst_dict = self._instance_info[host]
                         inst_dict["instances"][instance.uuid] = instance
-                    # Call sleep() to cooperatively yield
-                    time.sleep(0)
+                    utils.cooperative_yield()
                 LOG.debug("END:_async_init_instance_info")
 
         # Run this async so that we don't block the scheduler start-up

nova/tests/unit/virt/disk/mount/test_nbd.py

@@ -16,13 +16,13 @@
 
 import os
 import tempfile
-import time
 from unittest import mock
 
 import eventlet
 import fixtures
 
 from nova import test
+from nova import utils
 from nova.virt.disk.mount import nbd
 from nova.virt.image import model as imgmodel
 
@@ -304,7 +304,7 @@ class NbdTestCase(test.NoDBTestCase):
             # Ensure that context switch happens before the device is marked
             # as used. This will cause a failure without nbd-allocation-lock
             # in place.
-            time.sleep(0.1)
+            utils.cooperative_yield()
 
             # We always choose the top device in find_unused - remove it now.
             free_devices.pop()

nova/virt/libvirt/driver.py

@@ -11537,7 +11537,7 @@ class LibvirtDriver(driver.ComputeDriver):
         future.add_done_callback(thread_finished)
 
         # Let eventlet schedule the new thread right away
-        time.sleep(0)
+        utils.cooperative_yield()
 
         try:
             LOG.debug("Starting monitoring of live migration",