Always use sudo when calling out to virsh.

On some systems (at least Red Hat based), virsh connects to the libvirt
hypervisor as qemu:///session when run as non-root.  When root is used, virsh
connects to qemu:///system.  Inconsistent use of sudo with virsh (such as in
boot-seed-vm, but not in setup-network), means that the seed vm will not find
the brbm defined network when it is booted.