rhte-oc-cluster-vms: Fix reboot

Error is:

TASK [Reboot VM] ***************************************************************
Friday 07 September 2018  13:10:04 +0000 (0:05:02.849)       0:17:49.293 ******
fatal: [clientvm.ce4a.internal]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Shared connection to ec2-18-182-111-209.ap-northeast-1.compute.amazonaws.com closed.\r\n", "unreachable": true}
        to retry, use: --limit
        @/tmp/rhte-oc-cluster-vms-ce4a/ansible_agnostic_deployer/ansible/main.retry

'ignore_errors' is not enough because SSH connection is close by 'shutdown -r
now'

use async + poll=0 too.