prevent duplicate deploys and make pending deploys easier to spot

treat pending deploys like running deploys -> nobody else can start a deploy,
also giving them more visibility and preventing duplicate deploys when multiple people used to have pendin deploys

@steved555 @pswadi-zendesk @bolddane @jwswj 

### References
 - https://zendesk.atlassian.net/browse/SAMSON-113

### Risks
 - None
I want to tell them 422 so they hopefully try again later

On Thu, Oct 9, 2014 at 2:32 PM, Steven Davidovitz <notifications@github.com>
wrote:

> In app/controllers/integrations/base_controller.rb:
>
> > @@ -9,7 +9,10 @@ class Integrations::BaseController < ApplicationController
> >    def create
> >      if deploy?
> >        create_new_release
> > -      deploy_to_stages
> > +      unless deploy_to_stages
>
> not entirely sure we should care what we send back to the integrations
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/zendesk/samson/pull/139/files#r18675812>.
>