Support for token authentication (MFA)

[dalees]

Keystone v3 supports multiple methods of authentication, including password and token.
https://developer.openstack.org/api-ref/identity/v3/?expanded=#token-authentication-with-scoped-authorization

Currently, vagrant-openstack-provider supports password based authentication but this does not support OpenStack clouds that require token auth.

Example: CatalystCloud openrc requests and validates 2FA, then stores an environment variable OS_TOKEN for use by openstack commands instead of an environment password.