remove Docker stuff since it doesnt work
improve DNS test output
mail test: catch typical connecting errors and display nicer output
the bc package is no longer needed since redoing dns_update
the new dns_update totally forgot to write the OpenDKIM tables
refactor dns_update so that the zone is first generated in a file-format agnostic way
test_dns: more error handling
Vagrantize

* adding a Vagrantfile
* in a non-interactive setup like this, create the user's first email account for them
* let the machine auto-detect its IP address using http://icanhazip.com/
* use our own justtesting.email domain to provision a subdomain for users so they can quickly get started