lets a user set vagrant_provider config to control the provider used by vagrant to deploy VMs.
Merge pull request #130 from huit/feature/set-vagrant-provider

lets a user set vagrant_provider config to control the provider used by ...
Merge pull request #131 from huit/feature/integrate-scope

Feature/integrate scope
Compatibility changes for Cement 2.1, global scope

Various changes to accomodate Cement 2.1.  Using hooks for registry
loading and scope setting.  Fixing various scoping corner cases.