+- A new cluster attribute 'enabled_storage_types' is introduced. It will
+ be used to manage the storage types to be used by instances in the cluster.
+ Initially, it will be set to a list that includes lvm, file and sharedfile
+ if those are enabled. Additionally, it will include all storage types that
+ are currently used by instances. The order of storage types will be based
+ on Ganeti's history of supporting them. In the future, the first entry of
+ the list will be used as a default storage type on instance creation.