Ensure cuttlefish variable names match values

When showing lists of cuttlefish variables, we ensure that the
names match the values in the table cells and that they are in
the order requested by the user.
Fix match_key_order to not return `false` when the key is invalid.
* Also fix spec for get_valid_mappings.
Merge pull request #29 from basho/bugfix/show-config-variable-name-match

Ensure cuttlefish variable names match values