Support virtualbox and docker in the same vagrantfile.

[jsnshrmn]

No description provided.

[jsnshrmn]

this will also close #7 when it gets merged.

[jsnshrmn]

an open question for @Samwalton9 and @uyscuti-wiki:
This PR should enable docker to work while preserving the functionality for virtualbox (which I can't test).
I've updated the README to talk through the docker configuration and don't mention virtualbox at all since it's not something I can directly support currently. Does that seem reasonable? We could have both documented, but then somebody using virtualbox would have to be able to support/troubleshoot workflow issues for this.

[uyscuti-wiki]

Sounds reasonable. A couple of questions though:

1. does this PR alter the way we've been doing Vagrant/VirtualBox installations so far?
2. does this affect existing local vagrant environments?

[Samwalton9]

Received the following error when attempting to vagrant up from this branch:

There are errors in the configuration of this machine. Please fix
the following errors and try again:

vm:
* A box must be specified.

VirtualBox Provider:
* The following settings shouldn't exist: box

[jsnshrmn]

What vagrant providers do you have installed?

[Samwalton9]

How do I check that?