compatibility with Vagrant 1.5 config

Vagrant 1.5 doesn't seem to support `env[:global_config]` to retrieve your config however you can get this via `env[:machine].config` instead.

```shell
$ vagrant up
Bringing machine 'default' up with 'vmware_fusion' provider...
==> default: Cloning VMware VM: 'chef/centos-6.5'. This can take some time...
==> default: Checking if box 'chef/centos-6.5' is up to date...
==> default: Verifying vmnet devices are healthy...
==> default: Deleting the VM...
==> default: Running cleanup tasks for 'chef_solo' provisioner...
/Users/rjocoleman/.vagrant.d/gems/gems/vagrant-librarian-chef-0.1.4/lib/vagrant-librarian-chef/action/librarian_chef.rb:11:in `initialize': undefined method `librarian_chef' for nil:NilClass (NoMethodError)
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:90:in `new'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:90:in `finalize_action'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:20:in `block in initialize'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:20:in `map'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:20:in `initialize'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builder.rb:170:in `new'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builder.rb:170:in `to_app'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/call.rb:50:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:80:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:1018:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:95:in `block in finalize_action'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builder.rb:116:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/runner.rb:69:in `block in run'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/util/busy.rb:19:in `busy'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/runner.rb:69:in `run'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/call.rb:51:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/box_check_outdated.rb:60:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:1232:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:282:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:152:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:1097:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:472:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/handle_box.rb:56:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:95:in `block in finalize_action'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builder.rb:116:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/runner.rb:69:in `block in run'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/util/busy.rb:19:in `busy'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/runner.rb:69:in `run'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/call.rb:51:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:1232:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/lock.rb:42:in `block in call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/lock.rb:27:in `open'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/lock.rb:27:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:108:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:282:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builtin/config_validate.rb:25:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Users/rjocoleman/.vagrant.d/gems/gems/vagrant-vmware-fusion-2.3.4/lib/vagrant-vmware-fusion/action_farm.rb:169:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/warden.rb:34:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/builder.rb:116:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/runner.rb:69:in `block in run'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/util/busy.rb:19:in `busy'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/action/runner.rb:69:in `run'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/machine.rb:157:in `action'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.5.0/lib/vagrant/batch_action.rb:72:in `block (2 levels) in run'
```