Avoid vm instance shutdown when power state is NOSTATE

Occasionally when nova uses libvirt lib to query hypervisor
xen the instance state of vm_power_state may end up
with a NOSTATE value. Existing code shuts down the instance
when we hit this state. Remove the check for NOSTATE
to avoid shutting down the instance.

Fixes LP #1085771.

Change-Id: I0025f6800b6ca9cd3d7c7e6119b9a819571bd13c

nova/compute/manager.py

@@ -3001,7 +3001,7 @@ def _sync_power_states(self, context):
                 vm_instance = self.driver.get_info(db_instance)
                 vm_power_state = vm_instance['state']
             except exception.InstanceNotFound:
-                vm_power_state = power_state.NOSTATE
+                vm_power_state = power_state.SHUTDOWN
             # Note(maoy): the above get_info call might take a long time,
             # for example, because of a broken libvirt driver.
             # We re-query the DB to get the latest instance info to minimize
@@ -3052,9 +3052,8 @@ def _sync_power_states(self, context):
                 pass
             elif vm_state == vm_states.ACTIVE:
                 # The only rational power state should be RUNNING
-                if vm_power_state in (power_state.NOSTATE,
-                                       power_state.SHUTDOWN,
-                                       power_state.CRASHED):
+                if vm_power_state in (power_state.SHUTDOWN,
+                                      power_state.CRASHED):
                     LOG.warn(_("Instance shutdown by itself. Calling "
                                "the stop API."), instance=db_instance)
                     try: