Make molecule vagrant a collection: community.vagrant

As there is no official vagrant collection and we already have the most advanced vagrant module for it, we use this repository to ship two products:

* molecule-vagrant python package (already done now)
* `community.vagrant` ansible collection

As soon we have the collection published on galaxy, we will change the molecule driver to make use of it and avoid using the module directly as this does not work with execution environments.

A side effect of this change will be that molecule-vagrant users will be able to use the driver with any version of ansible they have as required collection(s) will be installed automatically.

I already asked @gundalow about this and he did not see a problem of publishing a `community.vagrant` collection from `ansible-community/molecule-vagrant` repository, as both organizations have the same community-first contribution models and security models.

The main benefit of keeping both products inside the same codebase is related to testing as testing vagrant on several platforms is very resource intensive. Having them split in two would make development very hard.

Anyone is welcomed to start working towards this goal. I will try to provide support, for example one repository that does something similar (dual collection and python package) is https://github.com/openstack/tripleo-repos

The issue does not name specific files or tests. Start by inspecting the repository packaging and molecule driver entry points, then compare the dual-package and collection approach in tripleo-repos. Done means the community.vagrant collection is published on Galaxy and the driver uses it instead of the module directly.

Written by the indexing model from the issue text.