script for configuring a vif in Xen in non-bridged mode

Creates a new vif device without attaching it to a
bridge. Quantum Linux Bridge Agent will attach the
created device to the belonging bridge.

Change-Id: I1818a92a47882d98e384b57e0fa84a0fa09d40ea
Merge "script for configuring a vif in Xen in non-bridged mode"