Allow to disable TSO on L3 agent nodes

When running Linux kernel 3.14, TSO/GRO could be enabled on compute
nodes to improve performances.

To improve north-south performances, this feature is needed on Neutron
L3 agent nodes.

This patch add TSO management for Neutron L3 agent and also
change the behavor for previous patch in ensuring that we use a kernel
>= 3.14 for both hypervisor & compute nodes.

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge pull request #610 from enovance/tso-controllers

Allow to disable TSO on L3 agent nodes
Check if VTX is enabled on hypervisor nodes

VTX is required when using KVM as hypervisor on compute nodes.

When the fact will be merged upstream, the lib/facter/vtx.rb file will be
dropped to use the one from facter-core.

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>