Add chef-vault environment specific helpers and LWRP.

/cc @schisamo @someara 

This pull-request is a work-in-progress; please do not merge yet! I am just looking to get some information regarding if this is something that is good to continue work on.

Adds support for an LWRP `chef_vault_environment_secret` which wraps data the name of the environment within the actual encrypted item. It also adds appropriate helper method for accessing such data.