Introduce support for 802.1qbg and 802.1qbh to Nova VIF model

Define the nova network VIF model properties for supporting
802.1qbg / 802.1qbh networking in hypervisor drivers. Also
wire up support to the libvirt driver for these new modes

Blueprint: libvirt-vif-driver
Change-Id: I91039790900170bfd698ea484d5f8a22445806ae
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Merge "Introduce support for 802.1qbg and 802.1qbh to Nova VIF model"