migration/colo: fix use after free of local_err

migration/colo: fix use after free of local_err

local_err is used again in secondary_vm_do_failover() after
replication_stop_all(), so we must zero it. Otherwise try to set
non-NULL local_err will crash.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200324153630.11882-5-vsementsov@virtuozzo.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
(cherry picked from commit 27d07fcfa70c3afa0664288cbce5334ed9595a3a)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>