Reverting default Ansible verbosity to default

I think the default verbosity of the Ansible provisioner should no longer default to `--verbose`. I personally feel it makes more sense to use default verbosity of Ansible and only increase if specified in the `Vagrantfile`.

This is effectively reverting https://github.com/mitchellh/vagrant/commit/ee9fc00a046f62efa5b9a63c061383644e55aaed. This change was made as part of efforts to resolve https://github.com/mitchellh/vagrant/issues/2194.