Set `PROPELLOR_DEBUG=1` in the environment, or `git config propellor.debug 1`
to make propellor print out all the commands it runs and any other debug
messages that Properties choose to emit.

Another handy debugging tip is to load up your config.hs in ghci, and look
at `hosts`. This will show the Properties of a Host, as well as the Info
associated with it, etc.
