
Rather than have to default it in tasks all over the place, we default it in group_vars. The default is to enable the feature if file-backed VM's are used. However, if there are no base images available, the set_fact task disables it. If a user wishes to force it not to be used, then an extra-var override is still usable. Change-Id: I5c916244a02a44da831d2a0fefd8e8aafae829b2