Implement rackspace auth for targets

[jmvrbanac]

We need to be able to control actions on Rackspace services. This issue should add support for authenticating to Rackspace services.

[jmvrbanac]

Updated the API blueprint for targets to accept a "rackspace" attribute for the authentication section. On implementation, Rift should store the auth information within the target document. On job execution, we should authenticate to Rackspace then retrieve the token and endpoint information required to conduct actions. While storing of auth creds in the DB is far from ideal, however, this is a temporary measure until we can get Barbican integration working.