Added unit tests for specifying the datastore.
Added unit tests for specifying the datastore.

briancurtin/pyrax,mandx/pyrax,pratikmallya/pyrax,rackerlabs/heat-pyrax,sivel/pyrax,ddaeschler/pyrax,vikomall/pyrax,rackspace/pyrax,naemono/pyrax,opsdisk/pyrax,roelvv/pyrax,0dataloss/pyrax,EdLeafe/pyrax