sr-iov: neutron-sriov-agent required for >= mitaka

[JuanJo Ciarlante]

Context: xenial/mitaka deploy using 16.07 charms release, sr-iov enabled as per release notes[0].

As per [1] compute node should "Enable neutron sriov-agent" -
without it, nova-compute fails with the infamous:

  NovaException: Unexpected vif_type=binding_failed

Got above fixed after manually installing the pkg and modifying
sriov_agent.ini as:

root@buizel:~# apt-get install neutron-sriov-agent
root@buizel:~# tail -3 /etc/neutron/plugins/ml2/sriov_agent.ini
[sriov_nic]
physical_device_mappings = physnet1:p4p2
exclude_devices =

[0] https://wiki.ubuntu.com/OpenStack/OpenStackCharms/ReleaseNotes1607#SR-IOV.2C_CPU_pinning_and_host_memory_reservation_.28Preview.29
[1] http://docs.openstack.org/mitaka/networking-guide/config-sriov.html

[James Page (james-page)]

The SR-IOV support was implemented across the charms against liberty (which did not require use of the neutron-sriov-agent). As of Mitaka, this agent is required for correct functioning of SR-IOV ports in neutron.

That said, this should not be a feature of the nova-compute charm; I think its probably a new charm (neutron-sriov) *but* it has to co-exist with neutron-openvswitch, so can't assume sole ownership of /etc/neutron/neutron.conf. As a result, this won't be super trivial to implement, as I suspect we'll need it to operate standalone on a compute node as well as with n-ovs.

[James Page (james-page)]

As a workaround, its possible to install the neutron-sriov-agent post charm deployment, and configure the physical device mappings in /etc/neutron/plugins/ml2/sriov_agent.ini inline with the nova-compute configuration.

[James Page (james-page)]

I also have an in flight change to fix this issue in n-ovs:

  https://review.openstack.org/#/c/396709/

however I'm currently blocked on testing due to bug 1641593