Bump development dependencies minitest & guard-minitest.
DataMunger, initial support for Driver configuration.
DataMunger, support driver name shorthand and explicit forms:

Shorthand:

    ---
    driver: dummy

Explicit:

    ---
    driver:
      name: dummy
      other: stuff
DataMunger - support provisioner configuration merging.
DataMunger - support busser configuration merging.
Refactor DataMunger and specs.
DataMunger - support legacy driver_config & driver_plugin style.
DataMunger - support driver, driver_plugin, & driver_config together.

Due to the way multi-YAML file merging happens, there may end up being a
data structure that contains `:driver`, `:driver_plugin`, and
`driver_config` all in the same location (i.e. in a platform, suite, or
common).

In case of current `:driver` and legacy keys, the newer `:driver` config
will win in the recursive merge and take precedence over the legacy
format.
Refactor DataMunger API method names.