Comment 49 for bug 1841189

Check the log of Peng，when the natbox fails to ping the instance after the instance is migrated, delete the this instance and re-create a new instance. At this time, natbox ping this new instance successfully. After migrating this new instance, natbox can still ping successfully.The relevant log information is as follows：

（192.168.120.26 is the instance‘s ip that natbox ping failed after migration）
controller-0:~$
[2019-11-23 05:12:31,087] 1654 DEBUG MainThread network_helper._get_net_ips_for_vms:: targeted ips for vm: ['192.168.120.26']
[2019-11-23 05:12:31,088] 1666 INFO MainThread network_helper._get_net_ips_for_vms:: IPs dict: {'a30dfd31-ed78-4a88-97d2-02aa762ff9ff': ['192.168.120.26']}
[2019-11-23 05:12:31,088] 2525 INFO MainThread network_helper.ping_server:: Ping 192.168.120.26 from host 128.224.186.181
[2019-11-23 05:12:31,089] 476 DEBUG MainThread ssh.exec_cmd:: Executing command...
[2019-11-23 05:12:31,089] 311 DEBUG MainThread ssh.send :: Send 'ping -c 3 192.168.120.26'
[2019-11-23 05:12:42,909] 433 DEBUG MainThread ssh.expect :: Output:
PING 192.168.120.26 (192.168.120.26) 56(84) bytes of data.

--- 192.168.120.26 ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 1999ms

（192.168.120.22 is the new instance’s ip, and this is the log before migration）
controller-0:~$
[2019-11-23 05:25:49,088] 1654 DEBUG MainThread network_helper._get_net_ips_for_vms:: targeted ips for vm: ['192.168.120.22']
[2019-11-23 05:25:49,088] 1666 INFO MainThread network_helper._get_net_ips_for_vms:: IPs dict: {'ea9e2ad0-b06f-4b5d-a3e9-bee87ac5f456': ['192.168.120.22']}
[2019-11-23 05:25:49,089] 2525 INFO MainThread network_helper.ping_server:: Ping 192.168.120.22 from host 128.224.186.181
[2019-11-23 05:25:49,089] 476 DEBUG MainThread ssh.exec_cmd:: Executing command...
[2019-11-23 05:25:49,090] 311 DEBUG MainThread ssh.send :: Send 'ping -c 3 192.168.120.22'
[2019-11-23 05:25:51,148] 433 DEBUG MainThread ssh.expect :: Output:
PING 192.168.120.22 (192.168.120.22) 56(84) bytes of data.
64 bytes from 192.168.120.22: icmp_seq=1 ttl=63 time=0.736 ms
64 bytes from 192.168.120.22: icmp_seq=2 ttl=63 time=0.664 ms
64 bytes from 192.168.120.22: icmp_seq=3 ttl=63 time=0.273 ms

--- 192.168.120.22 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1999ms
rtt min/avg/max/mdev = 0.273/0.557/0.736/0.205 ms

(This is the log information after migration)
controller-0:~$
[2019-11-23 05:28:17,789] 1654 DEBUG MainThread network_helper._get_net_ips_for_vms:: targeted ips for vm: ['192.168.120.22']
[2019-11-23 05:28:17,789] 1666 INFO MainThread network_helper._get_net_ips_for_vms:: IPs dict: {'ea9e2ad0-b06f-4b5d-a3e9-bee87ac5f456': ['192.168.120.22']}
[2019-11-23 05:28:17,790] 2525 INFO MainThread network_helper.ping_server:: Ping 192.168.120.22 from host 128.224.186.181
[2019-11-23 05:28:17,791] 476 DEBUG MainThread ssh.exec_cmd:: Executing command...
[2019-11-23 05:28:17,791] 311 DEBUG MainThread ssh.send :: Send 'ping -c 3 192.168.120.22'
[2019-11-23 05:28:19,869] 433 DEBUG MainThread ssh.expect :: Output:
PING 192.168.120.22 (192.168.120.22) 56(84) bytes of data.
64 bytes from 192.168.120.22: icmp_seq=1 ttl=63 time=0.465 ms
64 bytes from 192.168.120.22: icmp_seq=2 ttl=63 time=0.509 ms
64 bytes from 192.168.120.22: icmp_seq=3 ttl=63 time=0.621 ms