Destroy scatter_gather in conductor

Ensure destroy_scatter_gather_executor() is invoked during conductor
startup to prevent reuse of a pre-fork scatter_gather executor.

Change-Id: I62a01f51877001f19605762a1b8a09913b441dd2
Signed-off-by: Kamil Sambor <kamil.sambor@gmail.com>

nova/cmd/conductor.py

@@ -49,5 +49,6 @@ def main():
     workers = CONF.conductor.workers or processutils.get_worker_count()
 
     utils.destroy_default_executor()
+    utils.destroy_scatter_gather_executor()
     service.serve(server, workers=workers)
     service.wait()