Fix nonexistent staypuft_deployments params when services have no configuration

If there is no configuration for any service in step 3,
there will be no params[:staypuft_deployment] present.
This adds test if params[:staypuft_deployment] exists
to deployment_steps_controller when step 3 is submitted.
Merge pull request #47 from jtomasek/service_params_fix

Fix nonexistent staypuft_deployments params when services have no config...