Fix to create instance ip from subnet-uuid.
Also modified the port_create function in vnc_opentstack to use this fix

Closes-bug: #1369841

Change-Id: Id19efca8e0061a7564673b9e27ec3ba48172b00f
Merge "Fix to create instance ip from subnet-uuid. Also modified the port_create function in vnc_opentstack to use this fix"