Hook after `WaitForCommunicator` action if it exists

Vagrant 1.3.0 introduced (mitchellh/vagrant@261d0ef) new `WaitForCommunicator` action that ensures the VM is booted and ready for SSH connections. So hook after it if it exists. The default still stays to hook right after the `Boot` action.

Also fix the argument passed to [Plugin.action_hook](https://github.com/mitchellh/vagrant/blob/v1.3.4/lib/vagrant/plugin/v2/plugin.rb#L72) which should be *our* hook name (although currently not used for anything).