Add support for nodes.

Assuming a directory of `test/integration/nodes/` containing JSON files,
these will be added to the provisioner's sandbox for transfer to the
instance.

Note that this behavior is identical to data bags and roles in that a
suite-specific `nodes/` directory will be used if it exists. For
example, given a suite name of `client` the directory
`test/integration/client/nodes/` will be used for the provisioner's
sandbox.
Add `provisioner` support to .kitchen.yml and default to `"chef_solo"`.

For example:

    ---
    provisioner: chef_solo

    platforms:
      - name: ubuntu-10.04
        provisioner: chef_solo
        driver_plugin: vagrant
        driver_config:
          ...
Add Driver and Provisioner columns to `kitchen list` output.