Add VIF_VHOSTUSER

This is based on a new QEMU feature called vhost-user for connecting
to a user-space vswitch via a unix socket.

Change-Id: I0a11e89d3a0bbdfccac569c09009e576ea2e1173
Signed-off-by: Michele Paolino <m.paolino@virtualopensystems.com>
libvirt: enable hugepages config from flavor mem_hugepages

Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>