Add seed data

These seed data are useful during development, especially when working
with the UI and you don't want to deal with the overhead/hassle of
setting up actual nodes to manage.

Load them into your development instance by running:

    cd /tmp/crowbar-dev-test/opt/dell/crowbar_framework 
    rake db:seed

__WARNING__: This drops all existing rows in the `groups` and `nodes` tables.

You should then see something like [this screenshot](http://imagebin.org/index.php?mode=image&id=254394).