refactored node_layout to be more concise
style cleanup on node layout tests
style cleanup on ec2 agent
validating that users pass in one EBS/PD disk per machine in EC2/GCE
validating that PDs exist in GCE before using them
passing persistent disk info to AppController
passing over locations as a json dict instead of a colon-delimited string
unmounting, then detaching any persistent disks we added on cloud creation
specifying zone when validating persistent disks
correctly passing in --disks flag to run-instances
changed disk name to be consistent with what appcontroller expects it to be
terminating all services before trying to unmount the persistent disks
not passing over disks as flag option (since it is in nodelayout), and starting numbering of instances at 1 instead of 0
using correct device name when unmounting disks in gce, and not manually unmounting them at the moment
added exception handling when we try to unmount persistent disks