Summary: bring up KVM network bridge immediately

Detail: Users can experience long delays during VM migration, because the
linux bridge by default will have a forwarding delay set. This means that the
network will likely miss any gratuitous ARP from qemu notifying the network that
the MAC has moved. This change is a common reccommendation for virtualization
running on Linux bridges.

Signed-off-by: Marcus Sorensen <marcus@betterservers.com> 1357259186 -0700