Add fieri_key to ENV configuration.

If the fieri_key is set in the databag, set the ENV variable. This is used to
authenticate with Fieri requests. You will want to use the same key that is set
in the Fieri databag.
Allow FIERI_URL to be configured.

This is to support setting the location for Fieri.
Use nested attributes for Fieri.
Merge pull request #52 from opscode-cookbooks/fieri_key

Add fieri items to ENV configuration.