1. fixed conflation of user-data and cloud-init user-data. Cloud-init
user-data is now namespaced as 'cloud-init:user-data'.
2. user-scripts are now fetched from the meta-data service each boot and
executed as in the scripts directory
3. datacenter name is now namespaced as sdc:datacenter
4. user-scripts should be shebanged if there is no file magic