Key list refresh

Added library and knife methods for refreshing the key list for a vault item based on the saved SOLR search.  The knife vault subcommand is called 'refresh.'  Also added fairly extensive testing for the new methods in (and in the process made a few updates to) item_spec.rb and item_keys_spec.rb.

My org runs mostly on virtual hosts and hosts are created and terminated at a non-negligible pace.  We are also becoming increasingly dependent on encrypted data bags for managing secrets on the instances, but running 'knife vault update' every time a new client node needs its key added is absurd.  I had created a cookbook library that monkey-patched some of this functionality into it so the chef servers could refresh the keys automatically.  I've yanked that out and merged it into the current 3.0.0_working branch code.