VMware: support the hotplug of a neutron port

Nova already has support for hotplugging neutorn ports in the libvirt
driver. This extends the support to the VMware driver.

Implements the blueprint vmware-hot-plug

Change-Id: I01b78621016e20c8e61d48bdeeac166f08f799be
Merge "VMware: support the hotplug of a neutron port"