etcd inventory

I fought with the `smartdc` python package for 20 minutes or so and couldn't get it to accept my private key, failing with `ValueError('Unsupport PEM encryption algorithm')` :rage4:.  Sync from Joyent is working for now with `sdc-listmachines` output fed into the thing like so:

``` bash
ansible-inventory-etcd sync-joyent -j <(sdc-listmachines)
```
It'd be nice to document this path prefix.