[hacking] N374 do not use time.sleep(0) to yield

We have a centralized nova.utils.cooperative_yield() instead of
time.sleep(0). It is better as it allows to turn off the sleep calls
when the service runs in threaded mode.

Change-Id: I625daec79ee5b7f8b92116f450e21f997cef0546
Signed-off-by: Balazs Gibizer <gibi@redhat.com>

HACKING.rst

@@ -79,6 +79,8 @@ Nova Specific Commandments
 - [N372] Don't use the setDaemon method. Use the daemon attribute instead.
 - [N373] Don't use eventlet specific concurrency primitives. Use the one
   from stdlib instead. E.g. eventlet.sleep => time.sleep
+- [N374] Don't use time.sleep(0) to trigger eventlet yielding.
+  Use nova.utils.cooperative_yield() instead.
 
 Creating Unit Tests
 -------------------