Fixes #1822 Joyent list_machines is slower than it needs to be

[joyent|compute] list_machines unnecessarily fetches tags for each server
[cloudsigma] Add CloudSigma compute provider
[cloudsigma] Fix create request not expecting status 201
[cloudsigma] Make api location as an option (:cloudsigma_host)
[cloudsigma] Fix excon HTTPStatusError#response not having []= and failing on assignment of json decoded body