CLI: admin tasks (nodes)

[nphilipp]

Story

As an operator of Duffy,
I want to be able to manage nodes from the command line,
because talking to a JSON web API is such a nuisance.

Acceptance Criteria

A Duffy command exists

• to create reusable nodes (in: hostname, ipaddr, aux data)
• to update reusable nodes (in: hostname, ipaddr, aux data)
• to retire EOL reusable nodes
• to list active or all (+retired) nodes
• to show information about a single node

Background

Only reusable nodes need to be created on the command line, ephemeral ones (say for OpenNebula VMs) are created and retired on the spot by the Duffy task worker that provisions them.