This is part of the transition to using framework/log instead
of the Logf inside the framework package. This will help with
import size/cycles when importing the framework or subpackages.
Also, This change makes zone to work per datacenter and cleans up dummy vms.
There can be multiple datastores found for a given name. The datastore name is
unique only within a datacenter. So this commit returns a list of datastores
for a given datastore name in FindDatastoreByName() method. The calles are
responsible to handle or find the right datastore to use among those returned.
