add support to delete vm from specific hosted-service (dns).
method on same object no need to lookup.
fix multiple role delete and avoid find in alone_on_host to optimize
test case for deleting vm within a hosted service.
test case for multiple vm deletion using hosted service name.
Merge pull request #35 from opscode/OC-7837

Oc 7837 - Add ability to delete individual roles from a deployment in Azure