Neutron openvswitch agent running in compute node will control the
actual connection of the VMs in Dom0 via conntrack-tools, but Dom0
doesn't install conntrack-tools RPM by default.
This patch is to add such support with XenServer 7.0 and above.
Change-Id: Iec56db761015d4b7baa5a5f54314f4ff3fa67e02