Update node_groups to use scenarios

Currently node groups and scenarios were
kind of doing the same thing. For testing purposes,
the node group that needs to be provisioned is
determined per deployment scenario (at least for
the original mode)

This commit does the following:

- refactors node_group to use the scenario key for vagrant
- modifies the basic tests to use sed to set scenario
- changes name of node_group files to their relevent scenario name
Merge pull request #69 from bodepd/node_group_scenario_refactor

Update node_groups to use scenarios