Empty lists returned by the EC2 query should also be interpreted as errors.
Added minion keys pre-seed support to `saltcloud.utils.deploy_script`.

* Also support not deploying a minion.
* Return the `root_cmd` return code so we can stop the deployment in case of non zero exit codes.
Implement minion keys pre-seed in `saltcloud.cloud`.

* Differentiate from a local or remote master when deploying if `make_master` is true. This is because the remote master needs to get the pre-seeded minion keys, and those minions need to get the remote master PEM fingerprint along with it's IP address.
Implement the necessary changes to implement minion keys pre-seeding on a master to be deployed.
Implement master deployment to Digital Ocean along with minion keys pre-seeding support.
Implement minion keys pre-seed to GoGrid and pass the value of `display_ssh_output`.
Implement minion keys pre-seed to IBMSCE. Add `display_ssh_output` and `make_minion` deployment arguments.
Implement minion keys pre-seed to Joyent. Add `display_ssh_output` and `make_minion` deployment arguments.
Implement minion keys pre-seed to Libcloud AWS. Add `display_ssh_output` and `make_minion` deployment arguments.
Implement minion keys pre-seed to Linode. Add `display_ssh_output` and `make_minion` deployment arguments.
Implement minion keys pre-seed to OpenStack. Add `display_ssh_output` and `make_minion` deployment arguments.