Create an ignore file for Vagrant's configuration and internal files.

Documented at http://docs.vagrantup.com/v2/getting-started/project_setup.html

These files are created automatically the first time a vagrant box is started.
Allow the Vagrantfile to be tracked as that's the intended purpose.

From the documentation at http://docs.vagrantup.com/v2/getting-started/project_setup.html

"The Vagrantfile is meant to be committed to version control with your project, if you use version control. This way, every person working with that project can benefit from Vagrant without any upfront work."
Merge pull request #821 from healsdata/master

Create an ignore file for Vagrant's configuration and internal files.