express inventory create command

[jb4free]

create an inventory file of name in ~/pf9/pf9-express/inventory/name

that uses the default express template with no hosts.

[tomchris]

New data model needs to be created for this.
Inventory should be managed like config is now.
Multiple inventory's can be maintained on the same system.
Option to import and inventory
Look into dynamically assigned defaults for options. (ex. mgmt_ip can be default for cluster_IP etc)