[Zeta] Need proper cleanup for the static arp entries in DISABLED_create_auxgateway_test

[zzxgzgz]

The DISABLED_create_auxgateway_test testcase used to be NOT disabled, meaning that it will run automatically as one of the unit testcases.

However, in aca_CHILD container, which runs the unit tests before running the traffic tests, has the static ARP entries left after the unit tests. After running DISABLED_create_auxgateway_test, you can find the arp entries with this command:

docker exec aca_CHILD arp -n

and you should see that there's a MAC address of fa:17:3e:d7:f2:6d, if we don't clean this up, when we run the traffic tests(DISABLED_2_ports_CREATE_test_traffic_PARENT and DISABLED_2_ports_CREATE_test_traffic_CHILD), the issue #216 will happen.

If you install tcpdump on the aca_CHILD and aca_PARENT containers, and use this command to capture the packets, you will see above mac address associated with the wrong IP.