Enable oauth2 login

Replace openid provider with oauth2. Oauth2 provides more details about
user profile and contains profile picture url. This patch contains
the groups_oauth2 module, an oauth2 authorization implementation for Drupal
written for openstackid.org provider. See module's readme for required
variable settings.

Change-Id: I30fc363d60a5f679194dfd0f9d6c6453f783f9aa