iterate a bit on 'aws info' command

- get expected vpc and security group names from the elasticluster config
  and complain when they aren't present instead of relying on the user
  to scan the list
- remove us-east-1 hardcode by getting the aws region from the elasticluster
  config
- emit instance state (running, stopped, etc.)
- only emit instances in the configured vpc
- remove stale imports
'aws icel unmount' subcommand to unmount a lustre scratch filesystem