Use ssh connection caching, especially when bootstrapping.
propellor spin
propellor spin
propellor spin
propellor spin
propellor spin
propellor spin
propellor spin
propellor spin
propellor spin
revert
Propellor monad is a Reader for HostAttr

So far, the hostname is only used to improve a message in withPrivData,
but I anticipate using HostAttr for a lot more.
use HostAttr to simplify config file
propellor spin