Nova already has support for hotplugging neutorn ports in the libvirt
driver. This extends the support to the XenAPI driver, implement
attaching/detaching VIFs
I have made a patch to run releated testcase in xenserver CI
https://review.openstack.org/#/c/416797/
Change-Id: I22f3fe52d07100592015007653c7f8c47c25d22c
Implements: blueprint xenapi-vif-hotplug