Update Vagrantfile

The Vagrantfile had been mostly ignored until now. Update it with the
beginnings of variables for box name/url as well as some of the bits
necessary for install bits under Ubuntu. This will eventually be
extended to support other distros as well.
Merge pull request #20 from craigtracey/vagrant-update

Update Vagrantfile
Vagrant environment variables and fixed heredoc

Change the Vagrantfile variables to be overridable via environment
varaibles and fix a broken heredoc.
clean up the logger

As the _logger global variable should only be accessed from this file
alone, lead it with an underscore. Also set propagate = False.
Simplify logging

There is no need to manage the logger through a utility function.
Therefore, remove all that logic and just use the logging module
correctly.
Add Travis build status to README

As the subject says: add build status.
Refactor with builder support

Refactor the builders to so that a user may specify one of 2 paths:
system packages or docker containers. This change also encompasses a
bunch of other minor changes.  This is being checked in in order to
get some minimally viable changes upstream.