Fog not required...

Looks like this will happen on anyones machine that doesn't have a vagrant plugin that includes fog

Causing issue:

```
/Users/andrewwr/.vagrant.d/gems/gems/vagrant-adam-0.4.0a/lib/vagrant-adam/action/pre_provision_script.rb:3:in `require': cannot load such file -- fog (LoadError)
        from /Users/andrewwr/.vagrant.d/gems/gems/vagrant-adam-0.4.0a/lib/vagrant-adam/action/pre_provision_script.rb:3:in `<top (required)>'
        from /Users/andrewwr/.vagrant.d/gems/gems/vagrant-adam-0.4.0a/lib/vagrant-adam/plugin.rb:37:in `require_relative'
        from /Users/andrewwr/.vagrant.d/gems/gems/vagrant-adam-0.4.0a/lib/vagrant-adam/plugin.rb:37:in `block in <class:Plugin>'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/action/runner.rb:42:in `call'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/action/runner.rb:42:in `block (2 levels) in run'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/action/runner.rb:41:in `tap'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/action/runner.rb:41:in `block in run'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/action/runner.rb:40:in `map'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/action/runner.rb:40:in `run'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/environment.rb:346:in `hook'
        from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.3/lib/vagrant/environment.rb:145:in `initialize'
        from /Applications/Vagrant/bin/../embedded/gems/gems/vagrant-1.6.3/bin/vagrant:157:in `new'
        from /Applications/Vagrant/bin/../embedded/gems/gems/vagrant-1.6.3/bin/vagrant:157:in `<main>'
```