xenapi: freebsd and gentoo builds fail when using old agents

[John Garbutt]

The tightened up agent checking causes issues when building FreeBSD and Gentoo builds.

While the agent has now been fixed, instances with the old agent still fail to be built due to errors like this:
The agent call to resetnetwork returned an an error: {u'message': u"Couldn't restart network routing: 256", u'returncode': u'500'}. args={'dom_id': '116', 'id': 'f7167125-6ec0-4123-b0c1-8f2f16a42246', 'timeout': '60', 'host_uuid': '9a3766e7-4a7c-48cb-b9d5-a3d570cf3264'}

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/46051

[John Garbutt (johngarbutt)]

we have found a less hacky fix with forcing an agent upgrade

[John Garbutt (johngarbutt)]

the agent update has its own issues, we should probably add this workaround.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/46051
Committed: http://github.com/openstack/nova/commit/32ab0fc4056f59bd7841a7dac245249462648d42
Submitter: Jenkins
Branch: master

commit 32ab0fc4056f59bd7841a7dac245249462648d42
Author: John Garbutt <email address hidden>
Date: Wed Sep 11 11:35:30 2013 +0100

    xenapi: ignore 500 errors from agent resetnetwork

    Old versions of the FreeBSD and Gentoo agent return 500 on successful
    resetnetwork calls. This changes the current error checking to treat 500
    as a successful response for resetnetwork calls.

    Fixes bug 1223818
    Change-Id: Ia3eea109b6c3186af77124c704f13b70b0b91e81