Make Discovery plugable, add a disabled and Rackspace provider.
Allow overriding what metadata key to search for.
Add deps.
Add support for common env variables used for Rackspace Region, Username, and API Key.
Backoff hitting the cloud servers APIs if nothing is changing.
Allow javascript to search by any metadata key.
Call it noop discovery.
Remove dead return.
Merge pull request #40 from pquerna/plugable_discovery

Pluggable Discovery backends