ARP driver in astra-appliance needs additional exception handling

[Ryan Petrello]

The appliance has code that, at configuration time, looks at each network and removes ARP entries that no longer have networks associated with them. This can happen, for example, if a network is hot-detached from the backing Nova VM and the router still has a stale entry:

https://github.com/openstack/astara-appliance/blob/stable/liberty/akanda/router/drivers/arp.py#L151

This code needs some exception handling around the `/usr/sbin/arp -d` call; we've encountered a race condition where by the time `/usr/sbin/arp -d <ip>` is called, the stale entry has already been cleaned up. This code should probably be wrapped in a `try: except:` and ignored on failure (as it's just cleanup, after all).

This bug *only affects Liberty and prior; Adam Gandelman actually fixed it as a side effect in Mitaka during his work on keepalived HA:

https://github.com/openstack/astara-appliance/commit/02383adf645c479aba2838602c90fd5135fd0417

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/kilo
Review: https://review.openstack.org/317696

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/317696
Committed: https://git.openstack.org/cgit/openstack/astara-appliance/commit/?id=fcb3aa8c5b98346eecf4176aa6f2c293604f42ee
Submitter: Jenkins
Branch: stable/kilo

commit fcb3aa8c5b98346eecf4176aa6f2c293604f42ee
Author: Ryan Petrello <email address hidden>
Date: Tue May 17 10:07:49 2016 -0400

    Add additional exception handling to ARP cleanup.

    This was originally resolved in Mitaka via
    http://git.openstack.org/cgit/openstack/astara-appliance/commit/?id=02383adf645c479aba2838602c90fd5135fd0417
    Backporting this as it has the potential to break the router build+configure
    process.

    Closes bug #1582736
    Change-Id: If2ddbf5f2080b29c876e7750ba3b81f15ab3cc08

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/317490
Committed: https://git.openstack.org/cgit/openstack/astara-appliance/commit/?id=9d18b7e065b6be94c4428d768308d61924d86094
Submitter: Jenkins
Branch: stable/liberty

commit 9d18b7e065b6be94c4428d768308d61924d86094
Author: Ryan Petrello <email address hidden>
Date: Tue May 17 10:07:49 2016 -0400

    Add additional exception handling to ARP cleanup.

    This was originally resolved in Mitaka via
    http://git.openstack.org/cgit/openstack/astara-appliance/commit/?id=02383adf645c479aba2838602c90fd5135fd0417
    Backporting this as it has the potential to break the router build+configure
    process.

    Closes bug #1582736
    Change-Id: I630007e3fb9c33e0cac11ab39b95ba63434ed059