nova-make-compute-node-hypervisor-nodename-unique

in nova db, hyper-visor node_name is not set as unique by the nova schema. And is causing
invalid data while querying the hyper-visor related information such as servers. This blue print is to address this issue.

This causes error nova hyper-visor-servers <hyper-visor name> to list wrong details when there are more than on hyper-visors got registered in nova with same node_name.

This involve changes in the db model and update all appropriate hyper-visor's driver to take care of the uniqueness of the hyper-visor node_name.