Improve puppet logging

 - Log to a file as well as the console. Useful for grepping for errors
   rather than having to scrollback through terminal. File is deleted at
   start so it doesn't grow for ever
 - Add the verbose switch to give some more useful information, but not
   as much information overload as debug mode gives
Merge pull request #633 from alphagov/improve-puppet-logging

Improve puppet logging