Integrate PR#120 from Matt Brimstone, which adds the --clean option
to 'knife vault update' to remove client keys before re-encrypting with
the return of the saved or specified search query

Also added a basic Cucumber+Aruba testing framework, with step definitions
for setting up a repo, creating a vault item and testing whether an item
is encrypted for a given client.  Only the --clean switch is tested right
now, but this gives people a place to hang future tests that only affect
the CLI.