tests for a global config file
load global config and merge it
clean up tailor errors
Merge pull request #90 from thommay/gh31

Add a global config file
Expose provisioner in driver configuration.

Exposes a new config file option: provisioner.

Detects if it is being init'ed in a Module or a Cookbook and defaults to
the right provisioner.

Passed to the driver as the `provisioner` configuration
item.

Includes updates to docs and tests.