virttest.qemu_vm: Support ctrl_mac_addr parameter in qemu command.

Signed-off-by: Feng Yang <fyang@redhat.com>
virt.share.cfg: Update macvtap_mac_change configure.

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #1736 from FengYang/macvtap

virttest.qemu_vm: Support ctrl_mac_addr parameter in qemu command