1.Imply os-acc to attach or detach accelerator.
2.This implementation couples with libvirt, we must improve
it later.
3.Here is a patch of nova. I hope it can help to review this
commit.
https://github.com/wangzh1993/openstack_patch/tree/master/cyborg-os_acc-nova-patch/nova
4.Add UT
5.Remove unnecessary file.
6.Remove unused config in tox.
Change-Id: I140cb63549dbe2f70ac84122c569564193001e18