Added Sane Defaults!!

Allows for computed defaults for a select list of pre-determined
platforms.

Currently a .kitchen.yml file of the following would work:

    ---
    platforms:
      - name: ubuntu-10.04
      - name: ubuntu-12.04
      - name: centos-5.9
      - name: centos-6.4
      - name: debian-7.1.0

    suites:
      - name: default
        run_list:
          - recipe[something]
Whitespace.
Merge pull request #30 from opscode/compupted-defaults

Computed defaults